Re: residual pollen - it's possible, but not enough to seriously impact the plants. According to Rosenthal (all glory be unto him) if a plant is only slightly pollinated, it won't go into the whole systemic, no-more-growth-thanks-I'm-pregnant phase - most of the buds will continue in a sensi fashion, even if one or two pistils have been pollinated. It won't hurt to vacuum out and wipe down the area when you're done with your seed crop though.
So maybe round two gives you another 10-15 seeds before round three is free and clear - worst case scenario.