A lot will depend on what you are going to be shooting and the max distance with that 204 Ruger.
If you plan to hunt P-dogs at long ranges that may approach 300 or more yards, I would go for a high power varible such as the 6.5 X 20 you mentioned.
If you only plan to hunt coyotes & rabbits I would consider a 3X9 or 4X12 power. As for the cross hairs that should be one that you are comfortable with. some like du-plex and others prefer the mil-dots. Mil-dots can come in handy for hold over at extreme range and windage conditions if you learn to use them with practice.
If it is going to be a P-dog gun, make sure that your cross hairs are fine enough not to block out a P-dog at long range. Kind of hard to hit your target if you can not see it.
RELH