Check the tag on the Hobart. Keep in mind, it will be rated at 100% output, which you will NEVER reach. Also recommended circuit size (which factors in huge safety) and actual load are two different things.You'll be lucky if you ever reach 50% of the load rating. 50 amp is plenty for the machine you are proposing. As for wire, nope... 220 single phase takes three wires, the fourth is the addition of a ground rod. I did pound in an additional rod at my shop panel, because I tied in at the feed to the meter, not at my house panel. So, from the meter, the house is fed with 3 wires (mine from United Power), the ground rod adds the fourth wire you see in your panel. At my meter, United power has a main breaker in their box and it had room for a couple additional breakers. I added a 50 Amp (called them first and they said their source from the transformer was unlimited, so add any amp load I desired). Ran three wires to my sub panel at the shop, added a ground rod and grounded the panel (and the metal building). My 220 lift, welders, etc are all three wire connections. If you get power from xcel and you add a sub panel fed from your house panel, most inspectors want the 4th wire, connecting both panel grounds together.
The ground terminates at the same buss bar as the neutral. The ground was added to modern electrical as a back up for neutral that might go bad (break), leaving you as the source to ground. (the reason modern receptacles have three prongs, not two, like years ago) Single phase panels have 3 buss bars, the two the breakers are attached to are 110v each (on different transformer phases) therefore one 110v from each buss bar connected to a device will create 220v. The neutral is were any misc. unused power is sent to ground. This keeps the ground from shocking you if you touch it (like touching a metal drill). Now GFI's measure shorts and trip at 1/60,000 of a second (or something like that) so you can't get shocked from a short even if you stand in a bucket of water and touch the wires! and arc fault breakers detect an arc, in a switch, light bulb, motor, wire anything that arcs, but not necessarily a short. New in 2009 NEC and a pain in the but in the shop or anywhere a brush type motor operates (a vacuum cleaner), but again they trip upon detection of an arc of any type.
This is a very brief description of electrical. Call me if you want to talk in detail. Have several friends that are electrical engineers and a couple master electricians that taught me the ropes many years ago. Since, I've wired all the homes I've built though the years and helped many of my friends with theirs.