The treat indicator is the little sub that changes colors from green /yellow /red .Green is good, Red you are on the verge of being spotted or detected if not already.
Time compression is a great thing if you use it wisely. If you are in a danger area. go slow TC of 64 is about as fast a you want if you are trying to spot aircraft and you want enough time to react.
As for the aircraft issue, yes going that fast will somewhat disable aircraft. Go 250 to 512 and you will see plenty of aircraft .
