Here's too put it clearly. You have an ally with 1m attack stats. You can either divide it by 50, or multiply by .02 (this is 2% of the stats, either way). That number is now, 20k. You receive 20k stats as BFA to your attack.
100% of your BFA adds to your raw stats. To know how much of it converts to your BTA (bonus to allies), reference ninja's post above me.
Check the this link http://forum.kingdomsatwar.com/viewtopic.php?f=6&t=24806 for that, only certain quests drop xtals. The random drops on Quests are nobility points.
Quests also random drop crystals but the chance is much much lower. The exact percentage is not known.