Did you check that your MainGroup didn't include the Editor group? (this could be one simp0le reason or misconfiguration to produce that unwanted behavior).
And definitely, category permission, so far, allow only view and admin, but page permissions allow all the perms related to wiki pages (similar to other tiki features). They can coexist (and do pretty well). If they don't in your case, there must be a recent bug somewhere (that should be reported and fixed). If it's a bug, and it's kind of very important to you that somebody fixes it urgently, I'd suggest that you request a coder to do it, and pay him/her for that (FYI: I'm not a coder; I'm just sharing with you what I do in a similar case)
Beyond that, if you keep the Tiki track (I'd suggest so ;-), keep track of the workspaces feature (installable through AulaWiki Mod on Tiki 1.9.x sites). It contains a bunch of features to easily do what you are planning to do by hand.... (but try only aulawiki Mod and workspaces after you understand configuration of groups and perms: global, local, inherited groups, etc.)
For Workspaces manual and so (already translated to English), look for aulawiki on http://edu.tikiwiki.org
Good luck (HTH)