To get the lug bolt pattern, you would measure between alternating holes. So if you number 1 - 5, measure between 1 and 3, center to center. If it measured say 5.6", your rims would be 5 on 5 1/2 bolt pattern.
As far as adaptors go, I never have, but have know a couple of guys who have with no issues. You would have to take into consideration the backspacing of rim with the adaptors to see if they were enough or too much and wether you liked them or not.