1. MUI Prefs -> Scrollbars will get you set for MUI apps. I don't think the ASL file requesters' scrollbars (the system default ones) can be changed in a non-hacky way, but you could replace ASL altogether. There's an MUI version and maybe a few others.
2. Nope.
3. Snapshot the window while it's showing all files. Auto cleanup I'm not sure about.
5. I've never seen a case where NSDPatch.cfg has required any changes. I think the SetPatch arguments are correct.
6. If it works now, I say don't mess with it

7. It's an option in Sys:Prefs/Workbench.
9. I don't have any experience with BlizKick, but yes, I think you should leave out scsi.device. In fact, since you're loading in the 3.9 modules that way, change your SetPatch arguments to NOROMUPDATE.