Have at least one medic and one long-range soldier (a sniper, for example). You'll find that they'll get you through a lot.
Also, make sure that one other squad member also has Field Medic and Surgeon skills, in case your medic is the one who gets downed. I made the mistake of having my main medic take all the melee damage during the Highpool fight, which prompted a reload and doing the whole battle again.
But honestly, just make the squad you want. Go wild. Sooner or later, you'll find that literally everything will benefit you at some point. Yes, even Toaster Repair. In fact, especially Toaster Repair.