Some of these ideas should be handed to RDM instead of creating a whole new job. Their niche is buffing and enfeebling. Hastega should be a given. I'm not sure why RDM doesn't have Boost spells; Gain spells should just be deleted. RDM should have -aga of all enfeebling magic including native Sleepga. Spells like you suggested such as Extend, Quicken, Mute, Regain, Demi all sound like they should be given to RDM.

Lastly from your description, TIM looks like the job to kill off all current mages. There's no need to add another mage with GEO on the way as well.