you’re welcome. I’m almost certain you can’t apply for any long term visa inside of Thailand. The pros will chime in if I’m incorrect. You’d have to exit Thailand and apply for a long term visa. You could exit Thailand a couple of times then apply for the 30 extension also. But like I mentioned before, you will eventually be asked why you’re in Thailand long term without the proper visa.
there’s no limit per say by air. But saying that, if you are frequently doing it, you’ll eventually be asked question by the Thai immigration officer you face.
You won’t need it at Thailand immigration. You’ll more then likely need it when boarding the plane at your place or origin. That’s where the majority of people get asked about leaving Thailand within the 30-45 days.