to change from line E to line F direction Manhattan, do I exchange on the same platform?

Yes. The F and E run along tge same track at Forest Hills stop. The ONLY exception is if it's possibly a holiday or weekend and there's some kind of track work. In that case, look out on both sides of track to see what trains are arriving!

For the most part same track which is the Express track. Late night and weekends check on.platform to see which track it is running on.

Yes