Is the pool available to non guests for a fee?

I don't know the best way to get an answer that question is to actually call the resort

No

Yes you should be able to buy a membership for pool spa, etc. They have offered it for many years.

Last year there was a monthly membership fee to use the pool, spa, and gym. Not sure how much.

I think you can

I don't think so.

No. Unfortunately, you need to have a room key to enter the pool area