For testing OSes, get familiar with VMWare Workstation or VirtualBox. It saves a lot of headaches.
For storage, I've had good luck with D-Link DNS-321 and DNS-323. I like the power saving features of the D-Link and I've installed a few dozen of them as backup storage in the past. They work great for offsite storage because you can set the hard drives to spin down after 5 minutes and they'll spin up with you need to access them, be it through FTP, the built-in iTunes server, or UNC/Samba. Since the D-Links run their own embedded OS, they're not ideal for tooling around with other distros or hosting anything resource intensive. I only mention this as a storage solution if you are willing to go virtual for playing with OSes. Unless you really need the USB print server, just save the $100 and go with the DNS-321 over the 323.