Neh, Isollde's right. Blood Pact is on a 60-second cooldown by default, and can be lowered by some gear (primarily JSE50 and the Relic set, but also YYR as well)
In terms of stats, MP is obviously important (though hMP equally so). MND is decent for getting cap on Cure II and improving Cure IIIs, but the rest of the stats are virtually useless to the job; HP could be raised a bit to help prevent something like a stray AOE or dropped bomb from 1-shotting you, but isn't really important beyond that - I'd just recommend not wearing too much stuff that makes your HP dangerously low. -Enmity would also be semi-important since if you're main healing, the last thing you want to do is pull hate (again with the whole potentially-getting-1-shot).
-Perpetuation Cost is decent but a bit overrated - as Sabs said, you usually just toss out an avatar, BP then release, so you won't need to worry about it all that much since you'll typically only save ~10 or so mp. It adds up if you plan to leave your avatar out for a long time, i.e. when soloing, but then you typically use Carbuncle for that, whom will cost 0-1mp most your career if you have Carbuncle Mitts.
-Blood Pact timer gear has diminishing returns and is also somewhat overrated. While I'm sure many SMNs would disagree with me, I don't find having an enormous stack of -BP timer gear to have any practical use as you're generally are forced to rest a certain amount of tics to get the MP you spent from a Blood Pact back; if your timer is cooled off and you still haven't gotten the MP back from a L70 BP, for example, you either rest some more (thus making the -BP timer useless) or get up, resummon/BP (which at this rate will deplete your MP pool entirely). The only real time maxing out -BP gear is really beneficial is
-You have your avatar out constantly for L70BP spam, but that generally only happens if you're SMNburning something.
-You're using low-cost support buffs (but if you're in the Relic equipment range, the likelihood you use a wide variety of buffs is low, sticking you typically with Ward/Growl/Howl/[Hastega, huge maybe] for melee or Ward/Growl/DreamShroud for mages.)
Not saying -BP cost is bad or such, but getting past -10 or so usually leaves you with some MP not yet recovered. And in some cases it's just plain dumb. (Shame on SMNs who melee BP in YYR for the -5BP cost when SMN Doublet has 3% critical and -3BP cost.)
