With the .410 try to keep your shots inside of 20yds, but 10-15 or even less would be better.

1/2oz of shot out of a .410 is a pretty light payload, so you gotta go with #6. At ranges of <20yds, a head-neck shot with #9 will kill a turkey, but #6 is likely the smallest shot that's legal for turkey hunting.

Is there maybe a semi-auto 20ga around that you could borrow?