[Rataxes]

1) No, no type of illusion spell (not Imp Invisibility either Daniel) will protect you against casters who can see through invisibility.

2) Does being invisible prevent allies from casting beneficial spells on you?
Yes, not even your party members can specifically target you with any spells, offensive or beneficial, if you're invisible or "shimmering" (as in Imp Invisibility). You can, however, be affected by beneficial spells that target an area (ie Haste, Mass Invisibility, Prot from Evil 10'Radius)

3) No, no type of illusion spell can prevent you from casting a spell on yourself.

4) Yes, provided that the caster cannot see through invisibility of course.

5) Yes, if you go invisible after a caster (who does not see through invisibility) has begun to cast a spell specifically targetted at you, then it will be interrupted.

6) No.

7) The shimmering effect does not prevent Beholders from targetting you with rays if that's what you mean. Even though regular Beholders cannot see through invisibility, their rays don't count as spells.

8) It usually works, since you truly become invisible as opposed to just shimmering after taking an action with Mislead activated. Sometimes that small time frame in which you're visible is enough for a quick Beholder to target you with a ray though.

9) Yes, as does regular invisibility spells.

10) I couldn't imagine so, since they're red spells, but I honestly haven't tried this one.