Yep the latest Wiis can be hacked, I got mine christmas release updated to 4.0 with nintendo, then 4.1 with homebrew. With the 4.0 firmware to homebrew hack it you need the BannerBomb exploit.
2. BannerBomb like i said, its more devious in which it loaded from the actual system menu not with a game
3. Yep you can download ISOs off the web *I have, quite a few games* You use a WBFS manager, to drag and drop the ISO over. You can also back up your own games through the loaders out there
4. A few of the newer games do not work right away, a few tweaks and patches need to be applied, such as the 002 fix, SSBB works perfectly, wii sports, play and music work. The Wiiboard works fine, I have heard some trouble with motion plus, but again there are patches and fixes
5. The only brickifying homebrew i know of is, dodgy WADs, power failure mid update, If you use the correct homebrew and loaders the chances of a brick is very slim, I have been hacking my wii for a while now and the closest i got to a Brick was a failed install of a IOS (custom firmware to allow hacks) I reinstalled it and my Wii works perfectly.
Hope i set you on the right track with my basic knowledge