Are cards like A9o, KQo good enough to raise with in later position, even though there are 3 ahead of me? Can I assume that in most cases, these limpers are playing such a wide range PF that I am usually ahead and should try to knock one or two out of the pot before the flop comes?
Yes, this. Obviously reads are important here, I'd recommend getting the free trial of poker tracker 3 and setting up the HUD. Lots of these guys will be playing 50% of their hands. Go into pokerstove and look at 50% of hands and you'll notice they're playing some garbage hands. Punish them by raising.

If you have KQo and raise 6x bb after 2 limpers, they both call, and flop comes A72 rainbow, then most of the time they will just check it to you, you make a decently sized c-bet and take the pot. This makes you much more than limping and hoping to hit a K or Q. Most of them aren't complete idiots and will give you credit for big cards when you raise.