Leveling:
Still largely done by killing a mob over and over, but instead of 150-200xp ker kill on an IT+, you get an increasing amount of exp the more you kill a mob. In Zilart zones, that means Grounds of Valor books where completing a set number of kills on set mobs earns you increasing exp bonuses. In Abyssea, you start out by getting a tiny amount of exp per kill ramping up to 600+ per kill. And it takes about 15 sec or so to kill a mob. 150k EXP per hour is quite possible.
For GoV (Grounds of Valor) groups, it can take some time if others aren't leveling but if there are others in the zone, the it takes no time. You can be in an alliance and get a ton of exp killing EP mobs so if there is a group going, you should have to wait long. In Abyssea, there is ALWAYS an alliance leveling so you shouldn't have to wait long for that either, you just have to find them (usually in La Thiene Plateau [A]).
I could take a long time to explain the mechanics of leveling now, but once you get in a party it will all make sense quickly. Basically, you don't care about the per kill exp in GoV, you care about the page experience. (If you want to understand how GoV leveling works, look at my explanation
here.) In Abyssea, you might not get exp per kill at first but as more and more kills happen, you will get more and more exp. Again, get in a party, start killing and after a bit you will understand the mechanics. The good thing about WHM is you can contribute to an Abyssea party very early (70's) so since you are 75 WHM, just go there first. Most groups are always looking for healing magic.
Gear:
You buy pretty good gear from different parts of Abyssea. Some use cruor, some Dominion Ops points, some drop (I think all feet drop). So you want to look at the job you want to gear and look for the Empyrean set it uses, for instance your 75 WHM would use the
Orison set which can be upgraded to a
+1 and then a
+2 version. There is better gear that drops from Voidwatch but I have yet to participate in that so someone will have to tell you more about it.
I hope this was helpful to you.