Slapjack,
I get a lot of towels from TRC, and some from AG. I try to buy when on sale and have an assortment of different towels. I have only been doing this for a little over a year, and have already spent a ton of money on detailing supplies, and am only a hobby detailer. You learn a lot from this forum, but it's very easy to spend a lot to get where you're comfortable with the towels you need.
One of the best pieces of advice for me so far is when I was reading a thread where Mike Phillips said to buy wash mitts buy the ton. Whenever you place an order when there's a sale, buy a wash mitt. I have a lot and think you can't have to many. As far as towels go, there are so many different kinds that you have to experiment and see what works for you. I have found that besides AG, Larry Kosilla who has a great YouTube channel and his own line of products, which I can't mention here because AG doesn't sell them has great advice on microfiber towels in one of his videos. That being said, I think it's best to buy different towels when there are sales to see what you like best.
Alot of people here have the same story. Ive spent probably close to 10 grand in the past 2 years.