What should the first thing I do be when I get it? What should I put on the HUD, etc? I am a cash grinder and only play at like 5NL and moving to 10NL soon
Honestly, I'd say import what hands you have, and then look at every option and every tab and every report. We have great FAQs for the different features, and the more features you understand the easier it is to use PT3 effectively.
The Omaha module/version is not yet for sale as it is still in Beta. However, this means that if you buy the Holdem version you can use the Omaha module for free for now. If you haven't yet bought it you can use the 60 day free trial for both holdem and omaha.
Mac and PC are not separate purchases - you can use your license on two computers (that you own) of either type.