I have shot 3D for about 5 years now. I started out shooting my hunting rig and now I have 2 separate set ups. All of our clubs are ASA and I shoot Open class(unknown distance). I also shoot some indoor stuff. What it has done for me is it keeps a bow in my hand 12 months a year. And because of how much I shoot in the hunting off season it has made me more confident on my shots at animals.
I use Blackeagle PS23 arrows at 360g to get close to the speed limit for my class in 3D. I have used a fat 27 arrow in the past but it didn't seem to help catch any more lines than I was hitting with the smaller diameter arrows. My son couldn't shoot the fat arrows in his class so with me buying for both of us, it just made more financial sense for us to shoot the same arrow diameter.
Nothing wrong at all with shooting 3D with your current hunting rig and shoot "Bow Novice" to start with. It is a 30 yard max class. If you feel like its not a challenge, move up to Hunter class, which is 40 yard max. Both of these classes have certain equipment restrictions to keep it fair. For instance, Hunter class is considered a "Pins" class, which means you can't move your sight to shoot different distances. It also has stab length of less than 12" on front and 6" on back and speed limit of 280fps.
https://www.asaarchery.com/rules/pro-am-tour-rules
Our local clubs have created a "Hunter Movable" class for us hunters that use a movable single pin type sight because otherwise, according to ASA rules, you'd be stuck in the K40 class with completely tricked out target bows. Not fair to the hunting rig shooter at all.
Most importantly go out and have some fun killing foam........ but be careful, it can become addicting!!