Sounds good - personally, I wouldn't have them all in identical uniforms and equipment, I would have a bit of a mix-n-match feel to them.
For a good source of inspiration, take a look at BAS recent Merc pack (although they are uniform as you said), Edges resistance units, and the paramilitary forces that come with FDF 1.3.
A mix of drab olives, mixed camos schemes, some guys in sneakers instead of combat boots, some guys more or less in civvies (jeans and black T shirt), some with baseball caps, some with beanies - stuff like that.
Weapons - well, mercs pretty much have their pick, don't they? Maybe you could get permission to use some existing weapons packs, like Inquisitor's or the recent SOF2 conversion pack, E&S weapons, BAS weapons, SJB weapons etc.
P.S. If you get these units released, it would be great to have a Merc campaign, where you do different missions for cash, and then use your accumulated cash to purchase bigger and better weapons, hire men and vehicles etc.