Well, first off, I don't like it. But, it is
possible to do.
First off, you'd have to go by the Critter's base stats. That would mean average Physical attributes (all three's), NOT the magician's attributes. So, in your example, he'd wind up with 8's across the board. (Again, don't like this...)
1) Cannot go above augmented max for a Human. 9 is your limit.
2) I'd enforce this. If you're going to break a spell, then accept a limitation that you won't be able to talk.
3) No speaking at all. You do retain the ability to cast (per the spell's rules).
4) It sounds like it...
Here's how I picture it. If you cast Human Form, then you're reshaping your body into what you think the ultimate bad-ass combatant you can envision (Bruce Lee, Mr. T, Chuck Norris, Argent). However, doing so "warps" your vocal chords, preventing you from being able to communicate.
Some other things to consider when thinking about this:
A) You still don't have the skills to back up your new body. You are relying on your regular skills/defaults to perform the tasks. Sure, you might *look* and move like your hero, but you'll still have trouble throwing a punch like them.
B) Drain's cheaper on using Improved [Attribute] AND it goes off YOUR
abilities. You might not get all 8's, but in your example, you'd get the Reaction 9. Of course, you're maintaining four spells instead of one, but still...