The Mages Guild experience is not advanced by earning XP but by a fixed amount per lore book your find in the world plus additional XP for completing a library of a type of lore. For that reason, there is no bonus to finding each book with the use of XP potions or Crown Store XP scrolls.
Probably not, but do not worry. Judging from the fact ww/vamp skill lines appeared in the crown store, albeit unlevelled, The Monetization Department seems to be aware that skill/skill line progression is horribly undermonetized. Full-blown skills for cash P2W scheme will likely be introduced soon.