I would just focus on making the car safe, That is a huge rust hole, I don't know much about the early CRX if you can replace the subframe assuming its the same kinda setup as a 4th gen by all means do it. I would also research what autocross class you want to run and read the rule book, Changing the wheels and tires can sometime bump you into a class where you might not be competive. Make sure the brakes are tip top along with the suspension and tires and little things like the battery not straped down means you go home and don't run. Most important is to have fun and eat some VW GTi's