I have 125 cuft of c25. It doesn't last very long for my use. Depending on how much you'll be welding ij would go with that size or somewhere around double that. How close is the lws? Can you afford 2 bottles so you can just swap when one is empty? What kind of cart will you have? The 125 bottle is about 4' tall and 7" diameter. If yo usually use your machine when the lws is closed then get 2 bottles and keep a big bag of contact tips and an extra big spool of wire. I think that machine can handle 8-inch spools? Do you weld thick or thin? I stick to 035 wire in my miller 251 mig machine. But I'm usually doing thicker stuff. I have used it successfully to weld 20 ga sheet metal though...

Also, I have a Lincoln auto hood that i paid $130 for last year. I lie it. But I would look for something with 4 arc-sensors and a adjustable cutting mode plus shades 9-13 for welding and a grinding mode too. I think the digital elite from miller meet this. If your serious about this the spend some extra money on the hood. Completely worth it. Also, some good gloves are nice. I have some miller gloves and the quality seems to be low. The first pair ripped less than 5 minutes after I first put them on. Welding blankets can be useful to protect stuff near your work area. The magnets that look like arrows are good. Also, straight edges and speed squares. I have a dewalt grinder. I got it on sale. Work pretty decent. Keep a pair of ear plugs around. Grinding, hammering and welding can get loud at times. Soap stones are nice too for marking metal and drawing your blueprints on the concrete floor!

Oh, and just go burn metal as often as you can. Watch the videos on weldingtipsandtricks.com and practice what Jody says.