I have played a lot of demoman as well, almost over 400 hours and fully aware of the strenghts and weaknesses of the demoman
You are right in a lot of things, but some things you are wrong, also I will give some good advice on certain situations, not to critise you or anything, I think you made a good guide, just adding some more information
Everyone has a different style to play, like black_hand who is also known for his amazing demoman skill, me and black_hand both use different styles, what is best, is up to you to choose.
There are 2 main styles of playing the demoman, demoman who favor the pipelaucher above the remote, and the other way around, but lets talk about the tactics and advantages of one of the styles above the other, I personally choose the pipelaucher, it does a lot of damage, fast firepower also good for close combat. to give you an indication my pipe:remote kills are around 2:3 while black_hand has more 1:5
The range of the pipe is very important, if you have an uber, don't fire the pipes right away, the closer you are to the person the more the damage is, this isn't the case of the remote one, it takes atleast a second before it explodes and isn't as powerful since the update came out and lowered the offensive force of the stickies.
But that is just once side of the styles, remote pipes are a lot easier to use since you can choose to detonate them when they are close to a person, so it is easier to hurt somebody.
Sentryguns and protecting your own sentryguns:
The main target as Ballzac said, is to take out engineer buildings, but demoman are way more gifted then that, I've seen pyro's compressionblasting people around so it will be harder to take out your allied sentryguns, but the demoman can do the same, one good placed sticky can airlauch a person high into the sky, therefore making it harder to aim and most likely the sg survives, also a great way of helping out sgs is to put a sticky close to the gun, detonate it when there are 2 enemy stickies, the stickies aren't enough to destroy a sg when there are less then 3.
Also when taking out enemy sentryguns, it is most likely an engineer is sitting behind it wrenching it before it is even damaged, after him is a lv3 dispenser.
What do you do? Do not shoot at the sg directly, it takes about 4 pipes then and the engie and dispenser live, we do not want that, what do you do, move a bit to the side, and hit the engineer or the dispenser, this will cause with 3 pipes the destruction of both buildings and the engineer.
It is hard to aim when being a demoman because of all the sgs are shooting at you, your pipes will not always go where your cursor is at, remember that because you do not want to waste ammo or time. If you do it right, you can take away 3 sgs, even more if the engineers placed to close to eachother.
Keeping your distance is the most important thing of the demoman
As it says, the demoman is best at medium to long range, every class will die if you do it right, heavies aren't even a challenge, the spread is too much, demoman are the only problems then since they also posses the power to take you out from far away. Therefore if you closing in a corner, I will shoot 2-3 stickies to it and detonate it right before I come out of it, usually if you have a heavy/pyro/soldier waiting around the corner, they will be weaken and it is easier to take them out.
Also don't be a hero and start rushing, you do not have enough ammo to defend you all the time, keep your distance on the enemies.
Avoiding incoming shots
because the demoman has a decent amount of health, 175 but when healed 265 ( I think lol never pay attention to that) but it is more important to dodge the incoming shots even though you can easily take it, why? because of valve latest addition, a much higher rate of airlauching, if you are in the air, you cannot move properly and usually you die very fast, also shots that hit you will sometimes damage the medic, don't do it. Unless the medic is low on health then sometimes I will play personal cannonfodder just so he lives. So keep moving because it will also make it harder to headshot you, or for the spy to backstab you.
the demomans most feared class
Although everyone finds it pretty easy to kill a spy, it has one of the most powerful aspects of all, the backstab, everyone can do it, it isn't hard at all to get a backstab and you will die instantly, so keep attention for spies, usually when you get better and also higher in the rankings, you get a lot more dominations, and people tend to go spy to get a revenge kill, why? it is just as easy as that to stab a person, so always circle around to check if you see something suspicious. Also be careful for snipers, they can instantly kill you aswell, so keep an eye out, or even lauch a remote pipe to the sniper to airlauch him or use the smoke of the remote to shield you off a bit.
Another problem
Soldiers are also very challenging to the demoman, a skilled soldier is able to airlauch you in seconds, that means you cannot dodge anything or retreat so the rest of the team can easily shoot you down, so be careful things like that don't happen, you can either use the pipe or the remote, but I would go for the pipes since soldiers are slower, so it is easier to hit them and faster.
Using the ubers: Regular and krits
Sometimes it is much better like Ballzac to use kritskrieg rather than regular ubers, but first lets talk about the regular uber, if you are pushing, people always tend to go backwards? why? it is an instinct, therefore lauch with your remote laucher the stickies over them, soon 4 stickies lay right behind them and they will move into them, resulting in a quick death for them. Also when using regular ubers, go first for the sgs, then the people.
Also when you had the uber, usually you are all out of ammo, no problem usually you did enough damage to get a change of 25% to critical hit somebody with the bottle, ends up in an instant kill.
Also one of the things you see a lot are pyro's compressionblasting you, that is a big problem, since it is hard to aim, therefor if you are pushing and you see a pyro closing in, either alert your teammates to shoot/spam him down, or lop some stickies on the ground to airlauch/kill him.
Kritsubers: one of my favorite things when playing demoman, I sometimes had up to 11 kills in 1 kritskrieg round, especially at stage 3 on dustbowl, you can easily get up to 128 points with it, but also be careful, you shoot crits but don't get ambushed, shoot first a sticky to the corner so if anything comes he will die and you can use your pipe to attack after it use the remote stickies, also charging up 1 sticky is also useful for snipers in the back, lop it far over the other team to kill the snipers so they cannot headshot you or your medic.
Human shields
Using no uber, yet players are usually ubering terrible classes to take out a bunch of sgs, like soldiers, pyro's heavies. That isn't a problem at all, if the sgs are shooting down the ubered persons, take advantage of it and shoot down the sgs without any problems, this can also go for heavies with medics, they are living a lot longer so you usually have enough time to destroy the sgs.
The demomans greatest weakness if you are facing another demoman As discussed already airlauching is easily done by the stickybomb, if you guys are just hopping around it is hard to hit the demoman with a pipe bomb, therefore use a sticky, charge it up a bit so it goes faster and to the place you want it to be, at his feet, if he is airlauched, predict where he will land and fill the ground with stickies, usually this pretty much works on average/new demoman.
Corner sgs
Sgs are usually in places that are quite easy to take out, simply strafe left and right at the corner so the sg detects you, but doesn't have enough time to start shooting, 3 stickies is enough, but be careful the engineer doesn't run towards you and start wrenching you, therefore place 2-3 stickies at the wall so in case anyone comes, you can still protect yourself and try it again.
Dominating Ballzac
Join the opposite team
One of my favorite things, bottle the pyros!
Although this might seem like a stupid thing to do, it is actually quite easy and a lot of my bottle kills come from pyros. We all know pyros are effective but quite a "dumb" class (not offending but most players don't know how to play the pyro). Usually they just do W+Mouse1 and run towards you, but the advantage of the flamethrower is at close range, it hurts a lot, but if you circle around the pyro, he tends not to hit something at all and you will receive a very low amount of damage, usually 1-2 hits with the bottle are enough to finish him of. But try to damage him a bit before you go into a melee battle.
Another way is to airlauch the pyro with 1 sticky, then when he is falling down hit him with the bottle, if you do it right, he will get fall damage+sticky damage and the bottle finishes him off.
I am pretty sure I left a lot of stuff out, but this is just basic things, can't spread to much stuff, else I will dig my own grave.