increasing magic skills through training:
are the training increases based on the number of successful spells casts or on the total number of spell points cast? ie, would it be more efficient to cast 7 level one healing spells instead of one level 7 healing spell? is there any difference?

I don't know about the design of that, but fizzles and backfires do trigger Skill increases, and for Buffer spells already in place you get nothing. I'm pretty sure the engine counts both how much Mana you use and how many spells you cast, because when i cast a lot of little Knocks (or Charms) i get more increases than if i use up my Mana in one or two. I haven't made an analysis of the Buffers, though, and they may be counted differently. The Heal and Cure spells only yield increases if you're ailing, that's why some people like to train Water at that one gas-trap coffin in LM. Also, if you cast only enough to heal, then you cast less Mana, so you're less likely to get an increase, so i usually cast max every time someone needs a fix.

hmmm, well part buff spells are a different kettle of fish, but i did some experimenting with my monk (psionic spells) a locked box and the detet traps spell (mental magic realm)

after recasting detect traps lots of times i found that casting it at level 1 made me rise in skill points faster (per s.p. used and number of rest periods required)... but the actions of casting so many more detect traps at 1st level compared to a few 7th level it took longer in real world time.

with party buff spells i allways like to cast in the yellow, get the most benefit out of them with a not impossible chance of sucessfull casting. and many party buffs only take note of the first cast, till the spell wears off.
other spells have other pecularities. stamina only goes up if cast in combat, knock knock and divine trap can be cast as much as you want, hypno lure anytime. etc