Please consider the dangers involved when open wheel cars and fendered cars share the track at the same time. The visibilty issue: you are hard to see. The physics: You will lose if any contact is made. The speed differential: You will be faster than almost anything else out there in the corners and braking zones. If you are running with the TT'ers these will be "no passing zones" You will have to be very disciplined in order to get as many clean laps as possible, and minimize your exposure time.
If you can get your race liscense with the AROSC, do so. The racers seem to be very aware of the smaller, faster, harder to see cars. You will also be able to pass them where you can. I raced my FF with them at Las Vegas, the racers did an EXCELLENT job watching the flags and for me. I was about as comfortable with these guys as I could have been sharing the track with cars that weigh 2-3x as much. I wouldn't do that with too many (any) other groups.
One thing going for you while racing with them is, you won't be around them long. Doesn't interfere with your drive, nor their race.
VARA has some huge fields and you will on the track with cars of similar physical characteristics and speed. They would be (are) on the top of my short list. You'll get a lot of seat time for the buck with AROSC.
To answer one of your questions, I understand that TCRA allows open wheel cars to race with them. However, I wouldn't entertain the thought.