I agree with Gravedigger. If its explosions and destroying things, goblins are the way to go...Look around wc3 sites, there are loads of goblin models.
To "RPGsize" a game like this, I think you need a kind of shop where you can buy weapons(Sword, Mortar Shell, Sheep strike, ect). Every time you kill someone ,you get gold. Thats how you can buy weapons... To make this easyer, there should also be extra "creep" units (basicly and extra side) that moves between the rounds of the two players, and is controlled by the AI. This would mean that there is an alternative income to get gold, and through that, weapons.
The triggers that would make this round based seem pretty easy, so all YOU have to concentrate on is the filling (units, weaps, ect) in my opinion.
Good Luck, and if you need any help, pm me