If you're main concern is body work, frame repairs etc go with a wire feed, using a solid wire, gas shielded, not flux core. If you're a novice (no insult intended) it will be the easiest to pick up as well it's the most 'forgiving' as far as fit up, ability to weld to less than sound body panels and ability to fill holes, gaps etc.
You can get good results with a 150A machine which will run off a 50 amp circuit but check the welder specs first to confirm. I've got a 250A machine running off a separate circuit with no problems, (yet anyway), if you're after economy CO2 is the cheapest gas to go with ( be sure it's compatable/recommended for the wire you're using) use an .023 or an .030 S6 wire .
It's not a 'regular' wall outlet as such but it can be installed by any competent electrician.
By your third question I assume you're not a tradesman at least as far as welding goes, there are so many variables as far as looks, size of bead, base material condition goes that I wouldn't even attempt to answer that.
Be warned, there is more to frame repairs than 'sticking' it together, you have to be sure that you are not compromising the structural integrity/design of the vehicle. You would be leaving yourself open to a lot of grief attempting to repair someting you're not familiar with. I would you suggest that you get some training first, be it a course at a trade school or whatever. There are some things that just can't be repaired, safely anyway ...Mike