Demoknight with anything, even the caber and you got yourself a winner.
One trick that Crappy_Guerilla taught me: always have a sticky charging.
It seems simple, but it means that you always have the range to hit somebody far away, and you can just let go of the trigger and detonate immediately.

There's so much ammo in this game that it shouldn't matter. You should always be able to get more.

From observing, I can tell that you should get a pocket. As a medic myself, I can't think of anything more fun than Kritzkreig Demo.
!). I would just counsel you to get really good at one or the other. Both are very unique weapons and the learning curve is fairly steep for demo.Demo is great in all kinds of ways. You cant say he stinks at close range because if your good at pipes and predicting movements he could be really dangerous at close range. Work on stickies for the most part because thats usually easiest for most people to get better at. Use traps fairly often and try to be unpredictable when you play against people. Most demos are just spammers but if you play it right you can be super dangerous and never die.
Ah, yes. Sentries.
If you're ubered and running toward a sentry with the nade laucher, hit the sentry directly with pipes. If you don't have uber, use about 4-5 stickies, shooting from a place where neither the sentry nor the other team can see/get you. If you use enough the splash will get the sentry.
Do not, under most circumstances, spam m1+m2 stickies onto a sentry nest, unless there is a pyro that's really good at reflecting. If there is, change your trajectory a bit each time.
Loch....I haven't figured out the loch concerning sentries. I think two lochs kill any sentry.
Regarding minisentries: put all your practice into being pinpoint accurate with pipes to minisentries. One pipe will kill a mini. Make this your practicing priority, and minis will never bother you ever again.
Two hits? Pipe dat Texan.if you can get into a good position with the loch-n-load, you can annihilate any sentry plus the engineer if he gets too close. it takes down all, non-wranglered sentries in two hits.