Hi Dan,
1. Promotion through the tiers earns a small amount of credits. There are also free tournaments you can enter to try and increase your stash. However, that method can be a bit slow going. If you've played for a while and you like the game, consider upgrading. It helps you and it helps them.
2. Stroke play is available only on Bethpage Black and Kiawah Island courses for now. St. Andrews is in the pipe and will likely be available before the end of this month. New courses come out a little slower around here because of the time and expense to build them from the ground up. WGT is still a fledgling company and we all know that Rome wasn't built in a day. =)
3. From the game client menu, you'll want to JOIN A GROUP or CREATE A GROUP. Once you set your game options you'll be joined to a random group or you'll start a new lobby of your own. It's pretty self explanatory from there.
Welcome to the game and if you have any more questions, post 'em. Someone will help. =)