Regarding Therapeutics, you can hire Jayna Stiles (provided you have a free follower slot). She is handy for concocting the brews found in the "learned" (not "found") Therapeutics tree, and she also has Herbology to mix up cures.

Well, he doesn't have a pivotal role in the main story, but he has one of his own, which, IMO, is worth dragging him around. After a certain point, at the end of his storyline, he'll also get a major boost.

I ended up ditching virgil. i've only got enough room for 3 and a magic healer became farely useless for me. he was still effective in melee, but gar is better in that respect. jayna and magnus are great compliments to my tech char due to the fact that between the three of us we cover every tech field with the exception of explosives.
i've already decided to go through the game again as a charismatic elven mage after this run through. virgil will stick around for that one.

Note that followers will learn at most the first 4 schematics in any discipline. Also, they cannot craft found schematics.