Q173: are there any spells or magic items that increase the number of arms you have?
Check Arms of Plenty (Savage Species?). I believe it's distinct from Girallon Arms, but I may be incorrect.
Q174: Aside from Overchannel, are there any other ways to boost ML? I'm trying to get ML9 at level 6...
Assuming transparency, things that increase CL should work for ML too. Ioun Stones, etc.
This should be sufficient, assuming that transparency is, in fact, in effect.