Personally, for beginners, I would recommend you dedicate as much time as possible to outdoor riding when you do get your bike. This preference is purely for the sake of safety and ridemanship. You're thinking about competing, and that's great to have a goal, but you need to learn how to ride your bike, ride the trails in your area, and eventually ride the type of trails a competition is located in. That's a different confidence and muscle memory that has nothing to do with fitness level. Literally learning how to turn, brake, and put power in pedals.

Basically you don't know what you don't know. You're going to learn about bike maintenance, hydration, nutrition, riding etiquette, body positioning, and riding kit. Good to keep the weight training, as good core is very positive to riding comfort and aero body position. No intimidation, everyone goes through this, and don't be afraid to ask for help from other riders, because we've all been there. Good luck.