In the original game they have BP + MP = 10.
In some expansions they get buffed to a total of 12.
My personal experience, somewhere between 12 and 14, maybe 15, is good for the game.
My wizard gets +1 MP from the Talisman of Lore, +1BP +1MP from a wizard's cloak that I did not entirely invent by myself, and I plan to give him yet another MP from somewhere. My wizard gets 1 Spell per 2 MP, so if he has 6 MP he can take randomly 3 Spells from each group, if he has 8 MP he can take all 4 spells from each group. Yes. I have that many and plan to add two more per group so you'd never be sure what spell exactly you get when you choose a group.
The Elf can take randomly 2 spells from a elementary group or he takes all Elf spells. No more "i take water that has healing" because, if you want to be sure, you let that group to the wizard.
Realistic? no. Don't care.
For hero creation, me too, I would check out Slev, Mitchiemacha, Sotiris. Sotiris has no "system" but instead a lot of heroes to choose from.