RE: Pulling Manes
It sounds like your issue is that your horse's mane is unevenly thick along the length of his mane. Once you've let it grow out an inch or 2, try to pull it again, but focus on the thicker areas first to get a uniform thickness. If you feel that it's approaching the length that you want and it's still too thick, I usually only pull the "under-side" of the mane. For example, you normally grab a hunk of mane, teeze and pull. Instead, grab a hunk of mane, but separate it in two, the front part (which shows) and the underside. Just teeze the underside and pull that portion. This way, you keep the length in the front, where it shows, but are still able to thin the mane. You might end up taking a but of length this way, but not nearly as much.
To finish the pull job off, I always even it up with scissors. It's important to only trim less than 1/4-1/2" or less off and if it's looking too thick to cut, I may thin a bit with scissors (cutting vertically). Don't try to pull at this point, as then it will just be too short. I never want it to look cut, just naturally even, so only do this at the end of a pull job and show restraint in how much you trim :)
You also mentioned that your horse has a cowlick. I would recommend braiding your horse's mane over to the correct side and leaving it braided for 4-7 days prior to pulling and re-braiding as necessary. This may help train the mane and hopefully get that cowlick under control. You may have to braid after pulling or try keeping the braids in for longer periods of time to really train the mane, just see how your horse reacts to the braids to make sure he doesn't rub them all out!