You still havent started training yet?!?!?!?!
DUDE! Just listen to me - stop everything else, man up, and just START TRAINING. You will not regret it. The only thing that will get you in shape for bjj is bjj.
Just do it man, and don't worry about anything else. 300 is a great goal, but theres no reason to keep putting off training. You said you would start months ago. Lets go already!
The only reason I am ragging on you for this is because you already demonstrated such a passion for the sport, its time to take it to the next level already