Gators look really cool and play pretty good, but minions will be limited compared to full factions like trolls, as pointed out. I say start a combined force. Focus first on a minion army build with gator units that can work for trolls (all of them?) and just add trolls to that, as changing the casters changes everything. Granted, anything gators can do, trolls can do equally well, if not better...
Well, the trollblood in me says start with them. And, they have a starter pack with solid models in it. If you want them in the old metal, I have some trolls kicking around for credit or trade. Any extra 40K stuff, terrain, or maybe infinity stuff you don't want, let me know!
Either way, you will have a great deal of fun, and put out some EPIC damage in hand-to-hand.