If you want to start by using flux, just make sure your machine can run gas.
My first machine (and what i still use) is a Hobart handler 140. Its a 110v machine because i don't have 220v access, it has the most amperage of the big 3 (Hobart, Miller, Lincoln) while being cheaper than the others. I've used it on everything from a 1/2 plate for an axle truss on my jeep down to sheet metal on my electronics tray. I routinely use it for 3/16 and 1/4.
I also have used an Eastwood 110/220 machine that I was originally dissuaded by others because it wasn't from the big 3 but I have used my friends and I liked it a lot and its holding up just fine. I want to learn tig so I want to look into the Vulcan machines.
(before anyone yells at me for the 1/2 plate thing, it was a nonstructural bridge tying a bridge to the pumpkin on my axle truss. It was done with like 9 or 10 passes with a crap load of preheat and post heat)