Sorry, you can't multi-cast Wizard's Communion and double your level. The text of the spell describes what it does, and it counts magi and "the level you know." I suggest it should be written as the level you cast, since you might know multiple versions of the spell, since it is a general spell. Even if you were to cast multiple copies, you are still 1 magus. If two rituals were going on simultaneously, you could certainly aid both rituals with a multicast Wizard's Communion. I don't see a problem with that.
There's been Errata on Muto Vim, and I've brought it up in the saga before. I'd mentioned previously (read about 3 or 4 posts between qcipher and myself), having Wizard's Communion being of Sun duration, subtracting 10 levels (for the increase from Momentary to Sun) from the effective level of the Wizard's Communion cast.
In light of that, I suggest you have Wizard's Communion at 25th level, without mastery. You would have a casting score of 13 + 5 for the Aura of 18. Even without an aura, with a casting score of 13 you can only fail on a botch (and it would be stress for assisting with the Aegis) or a 1 in a non-stress situation. You add 15 levels of power to the pool for doubling the spell's level.