Those FAILS on opening Screenmode prefs mean nothing - just that you don't have anything set for those Tooltypes, so nothing to worry about there.
At any rate, that's a lot of hacks you're running. ReqAttack, SystemPatch2, StackAttack, VisualPrefs, Executive, and FBlit are probably the most hacky. Check again that they're removed from startup-sequence and user-startup. Also check the WBStartup drawer. If I had to guess, I think VisualPrefs is the culprit.
Normally, when changing screenmodes, a requester pops up asking you to close all windows except drawers In other words, drawers can stay open, programs can't. Sometimes even iconified programs need to be quit or moved to another screen. It sounds like something is preventing that requester from opening and Intuition is hanging as a result.
By default, SnoopDOS doesn't show everything that's happening. Go to the functions window and enable everything - it might give you some more hints.
