Hi Clarisse,
Welcome to the world of resin! It sounds like you are trying out things and having fun. That’s awesome!
No, it’s not necessary that you fully sand your resin charms after demolding. Yes, sand off sharp edges so no one hurts themselves, but otherwise, if you are happy with the finish, then leave it alone.
Resin is a journey and it’s going to be a few months before you feel like you’re not just ‘making a big mess’. This four-minute video on our youtube channel will help you with a little perspective on what it takes to get good with resin. https://youtu.be/N3pgn_0mQks
Enjoy the journey!