imho, 10 awg and 30 amp breaker is the way to go. Since you're not getting any advice, other than hire an electrician, I thought I should throw in my diy advice. My reasoning is that a 20 amp motor will probably pull a little more amperage when it first kicks in. I'm assuming it's a dedicate circuit. It should be.
In other words... Yeah, I'd do what you're doing.