Some great advice here. Your thumb hole is one thing that you definitely want to feel consistent. It's also personal preference, so if it works for you, then it's right.
Personally, I am not a fan of the changeable thumb inserts, but many people are. I still pour a mold (20 minutes to set up) for all my thumb holes. I also love white tape for it's textured feel so I leave room in the hole for that.
Mine starts with a silicone mold of a favorite thumb hole, then I pour the resin around it (in a tube) and insert it like a pre-drilled slug, so to speak.
Last year in Baton Rouge my thumb was pretty swollen due to the climate (and perhaps my diet while there). I was extremely glad to have the extra room in the thumb hole and all I did was remove some tape. Good luck as you find out what works best for you.