Should use a 30 amp breaker for 220v/230v. I wouldn't advise using 2 single breakers because if one blows the other one stays on, it may damage your welder. As far as your wiring, 10 gauge is ok for 30 amps, but if your putting in a 50 amp plug, you might want to go 8 however it may not fit in your 30 amp circuit breaker.
It sounds like you have done your homework, however, on most 220 single phase applicatons, you don't use the common, just the ground, but not knowing your machines needs, it may be wired differently. Buddy up to an electrician <img src="/forums/images/graemlins/patriot.gif" alt="" /> and maybe for a sixpack he'll walk you through it.

Be careful and remember, I'm not responsible for any fried wires or body parts, just offering some ideas (disclaimer)

I'm jealous you got a miller welder <img src="/forums/images/graemlins/baby.gif" alt="" /> <img src="/forums/images/graemlins/frown.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" />
Everet <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" />