I agree w the Teflon mats! It is super dependent on your preferences and oven though. I’ve tried parchment and silicon before and I just don’t like the look or the risk of undertaking. I get the matte kind of Teflon on Amazon and have never had issue but a lot of people on the Facebook groups recommend the glossy type that you can get either on webstaurant or Ali express. I believe it’s mostly just that the glossy kind is more nonstick but again I’ve never had any issues w the matte kind.
I also recommend getting a set of piping bags with a large round tip if you don’t have one already. I started off with some cheap little plastic tips I had lying around the house and they were decent but having a nice metal tip made “cutting the batter” much neater. Other than that there’s not really much equipment or tools that you need. Indulge with Mimi has a lot of different templates that you can print out and since the Teflon sheets are quite thin, you can lay the templates below the sheets while you pipe and slide them out before baking.
Provided your ink has been allowed to dry completely, you don't technically need something in between, but best practice to avoid causing shine on the fabric or scorching is some kind of press cloth (a piece of thin cotton like muslin from Joann would work). You can also iron the item inside-out.
You can also use a Teflon sheet like these. Just be aware that they reflect moisture so if your ink isn't completely dry, it may affect the cure.
I use a whole on for regular sized things and when I do onsies or dog bandanas or other small thing I use one I cut in half. They work really well.