Hello! Other members have posted with similar questions/concerns before, so you're not alone. Most people usually advise that you go slow in case you have regrets. I personally have a very small collection (15 ponies), and I LOVE it . . . maybe think about which ones (if any) you really love and sell the rest. Then if you decide you're really done, sell what you've put aside.
Most G3s aren't worth much, so I'd do lots unless the ponies are especially sought after/valuable. Remember that your time is valuable--listing ponies singly takes a lot of work, plus you have to package and ship them all singly, and handle all those messages . . . anyway, something to consider!
Best wishes and best of luck!