a) The mechanism in the manual explains this quite accurately, although as I don't have the manual to hand I can't type it out. It isn't a case of diminishing returns, though.
b: No. There are less high level sites. Search level is not directly linked to rarity.
c: Sites are determined at game start. The game more or less rolls sites in each province until a roll fails to generate a site, IIRC.
d: Regen reduces hp loss to 1/year, rather than completely negating hp loss.
e: Welcome to spellcaster AI
Making sure there's only one group of soldiers in range of a buff helps a lot, as does the hold and attack order.
f: Yes.
g: Domes have a chance to intercept any spell cast directly at the province they inhabit. So assassin spells like Earth Attack can be stopped. As can friendly units trying to get in via teleport.
h: It's a risk, yes.
i: There is probably a list, but I don't know it.
j: Interesting - I don't know the answer to this one.
l: Don't know off the top of my head.
m: If you want researchers to respond to attacks on their province, don't build a castle for them to hide in. Cross-reference with h: above
