My broker allows 500/contract with a 2500 opening bal in the acct and it can drop lower once its opened. If you drop to 1000 overnite you get shut off. They also use an auto shutoff intraday if you lose a certain dollar amt or % of the acct intraday. They monitor because they dont want you to go negative and owe them money--which can really almost never happen if you use stops.
You need to close out by 415pm EST.
It costs 6.30 per contract round trip incl exchange fees which I think are an additional cost on that Think or Swim price.
Shop around.
My broker also offers a great chart platform -- Sierracharts for just a few dollars/mo and no platform fee.