I am not an expert, just someone who researched this when I did my control panel.
You can use 8 gauge, but thicker is better(at least that is what she said). A stove cord is probably 8 gauge, dryer cord probably 10. If you are pulling 30 amps, you "should" use a 30 amp breaker. If you are going to use a 50 amp, make sure all your wire is rated for 50 amp. So in your control panel, instead of using 10 gauge, use 8. Can you use a stove cord in the wall? I am sure it violates some code. I think my Home Depot has 6 gauge 4 wire romex for 4 a ft, 8 is like 3.79.