This is, in and of itself, the "final word" as far as your saga goes. If that's how magic works in your SG's saga, then that's how it works. That said, here are my opinions:
I believe that this should simply be ReCo, since the only thing that is being directly affected by magic is the location of the target's head, and doesn't do so in a way that DIRECTLY causes a worsening of the target's natural form. The fact that the target drowns in water is irrelevant. To turn the argument around that "this should require a Perdo requisite because it causes harm" - would the spell lose the requisite if the target could breathe water?
ReAq, for the same reasons as above.
I'm afraid you'll have to explain "direct and simple" here, for me to provide a reasonable opinion.
I wouldn't put a Pe requisite on these, for the same reasons listed earlier. Would a ReMe spell that caused a target to spill his innermost secrets require an Intellego requisite? Would a ReMe spell that forced a magus to cast a CrVi spell thus also require Creo and Vim requisites?
Oh! Thanks! Im glad... No im happy to hear that someone have a simillar thougths.
Same as personal guard against fire, or wood or animals
Not allow to pass air through the ward so you will sufocate unless you have any kind of muto or creo magic.
The same to put a circular ward against humans to keep the human imprisionated and then just pericentrical the second ward against air. Lets sufocate
Small problem with the ward against air is that the medieval paradigm, and Auram, doesn't really recognize air. At least not as a substance in its own right. Wind, sure. Smoke, fog, clouds, yes. Odors, even. Air ? The spell would work, yes, but it would take a very unusual magus to think about creating it in the first place.