2) You are correct, nothing gets passed M*2 for spirit caps. If the player persists in the argument, you can always give in to your players and have the spirit use edge against the summoning test. Do that a time or two and he'll either learn o roll up a new character.
Agreeing with you. Per the description-
"Spellcasting: In a pinch, you can spend reagents to
set the limit for Spellcasting. Rather than using the spell’s
Force as the limit, use the number of drams of reagents
spent."
I don't see anywhere in that statement that says you can exceed the natural Force limit of casting (Magic*2), just the dice limit (as in usable hits) of the spell instead of the Force it was cast at.