I have to agree with the crazy cajun; doing work like suspension upgrades or axle trussing isn't a good time to learn to weld. If the welds fail on a suspension bracket at 70MPH it can result in a very bad day on the highway, and if you don't know what you're doing you can easily warp your axle burning in a truss (I've seen even experienced welders do that).
Go to a metal recylcler and buy a bunch of scrap. Take a class at your local votech or community college. Practice until you're comfortable before tackling the Jeep.
You will need a 230V welder to do the truss, particularly if you're welding to the pumpkin. You might be able to get by with a 120V welder for the suspension brackets but you'll be fighting a battle between going slow enough for proper penetration and the duty cycle of the machine.
You can use flux core (FCAW) to weld your suspension brackets and truss. You will just have more clean-up work to do in removing slag and dealing with spatter. Heck, you can even stick weld it if you want. Provided you have the right technique and enough juice (Amps) to ensure good beads the main differences are speed, appearance and clean-up.
As for beginner machines, I'd suggest the Hobart Handler 210 MVP, Miller Millermatic 211 or Lincoln Power Mig 210 MP. All of these machines are made in the USA, will do gas shielded or flux core processes, and can run off 120 or 230 V/AC.
The Lincoln is a new but interesting machine as it can do stick, mig (gas or flux core) and tig for around $1200 (extra cost components needed for tig).
Hobart and Miller are from the same company. The Hobart 210 MVP is the least expensive at around $900 and is a pretty solid machine and the Miller 211 runs around $1200. The difference is the Miller has continuous-adjustable voltage vs the Hobart's 7-step voltage adjustment, the Miller has an "autoset" feature to help newbs set a good wire speed and voltage, and less plastic is used on the Miller (though newer Hobart 210's do have a metal wire feed drive mechanism).
Which is best is a religious discussion no less contentious than Windows vs Mac. The shops and experienced welders I know all prefer Miller for mig machines. I have an old Lincoln tombstone stick welder (bought used) that I play with and it works fine for what it is. Which leads me to another suggestion: check Criagslist and see what's available used in your area. This way you can start off cheap with a beginner machine and move up without losing a lot of your initial investment.
