Attributes are 3, 6, 9, 9. So raising two things by two upgrades each would be 3, 6 in one and then 3, 6 in a different one (total 9+9 = 18). Raising one thing by four upgrades would be 3, 6, 9, 9, total 27.
Combat skills and magic skills are relatively painless, it's 1, 2, 3, and then stays at 3 until you hit your limit of how many upgrades you can plunk in. So six dagger and three evasion upgrades would be 1, 2, 3, 3, 3, 3 for dagger and 1, 2, 3 for evasion (total 15 merits for dagger, 6 merits for evasion).
HP and MP add up almost as painfully as attributes. If you put all seven into one thing, you're looking at 1, 2, 3, 4, 5, 5, 5, total 25 for +70 HP or +70 MP. Of course, these do kick in on lower level jobs (they all do, of course), and HP and MP are more universally useful than any particular stats.
I second Skaw's recommendation of staying on experience mode, letting your buffer fill up, and then automatically getting limit exp after that. Particularly if you do something like Dynamis or CoP missions and die a lot. You don't want to be that person who's always delevelling to 74 and inconveniencing everyone by insisting on an R3. Go get full buffer, 44K exp sucks but then it's over and done with and you just have to maintain it from the exp you lose if you die.