1) As long as you do all the "Technical" stuff on a throw away account, and just enable HAN on your main account to play games you should be good. If it was easy to get a ban I think you would see a lot of complaint threads about it.
2) I followed that guide and had no issues with a few PS2 backups (SSX3, Megaman Command Mission)
3)I know you said other than backups but PSP games is nice even if the compatibility is so/so still add a decent number of games (FF7 Crisis core, JeanDeArc, Prinny are some notable ones) I have a PSP and a VIta and Im still thrilled to be able to play on a bigger screen.
-Custom XMB Waves is nice with Han Toolbox, a couple of them really look nice and its a nice change from the normal one.
-Custom Boot/Sound, again not a huge thing but nice to do.
-Ability to to sort and customize your library into a custom folder system with multiple folders in a folder, and you can do it on your PC and just import it into PS3 (This one is huge if you have a big library, I have 1 TB + PSN games not including backups and that list can get daunting. Right now Im working my way through my library Folder 1 by Genre with each genre having its own folder/group and some genres being broken down into even further folders. Folder 2 By Console with folders in each for each gen PSX,PS2,PS3,PSP) Folder 3 All games with Folders for each letter/group) and you can use custom images for these folders.
-The ability to mod backups (English patches, game fixes and tweaks for extra hard modes etc.) I havent messed with this but I know when I was big into PSP getting some JP exclusive games in a playable state was nice, if your into those types of games (Valkyria Chronicles 3 Im looking at you)
Im sure there's more technical stuff but that what I've spent my time with so far in the first week.
There's also others things that may or may not come in time, homebrew, emulators, etc.
I'm really hoping to see if a Remote play to PC hack comes out. Seems its a popular thing to happen with hacked consoles, well at least handhelds. (N3DS got it, PSVita got it, PSP was plain emulated). Its already possible with a handful of games , but something to unlock it for everything would be nice.