I have 120+ games on Steam. I've been playing PC golf games since Mean 18. As such, I have a perspective as both a hardcore gamer and as a golf sim fanatic. First, you have to decide what the model is going to be - a typical software game or free-to-play / pay-to-win. You're not going to be able to successfully to have both. You're not going to be able to charge $30 for the game, $10 for DLC packs and get a subscription fee or other micro-transactions. That would be an instant market failure.
The typical software game is like the old Links games. Game + DLC is how you make your money. Online features in this model would be basic and free. The upside is that it's a familiar model to PC golf gamers and you make your money when you sell the game. Considering you're trying to put the game on Steam, you'd price it accordingly (probably around $30) and then your courses become DLC released on a regular basis. There's no micro-transactions involved (clubs, balls, etc.) unless those micro-transactions are cosmetic only. This is the most typical model. After a while the sheer cost of the game + DLC becomes a barrier to entry. Adding a monthly subscription in this model is possible, but that becomes problematic because there's relatively little to offer with a subscription. It looks like a money grab to charge for the game, DLC and then try to tack on a monthly sub fee for what amounts to little more than multi-player tournaments.
The other model is the free-to-play / typical pay-to-win model. WTC, Pangya and others have tried this model with various degrees of success. The game becomes free because the idea is to get as many people playing it as possible and you sell clubs, balls, upgrades and more. I despise this model. In this model, skill invariably loses out to "whales" who upgrade the hell out of their character. I won't elaborate more on this model because this is NOT what Andrew said PP would be and if it is I won't play it at all. Not to mention that it doesn't generally fit with having a course designer. The rewards in this model can be enormous if you capture enough whales,
Now there is a bit of a third option that can fit in with either free-to-play or the typical software game model. It's been done with MMOs like Guild Wars and even generated massive revenue with free-to-play games (that isn't pay-to-win) like Path of Exile. That's selling micro-transactions that have no tangible impact on the game. New avatars, clothing, interesting graphical effects, etc. In fact, Path of Exile exists solely on these types of transactions.