RE: scuba regulator
scuba regs are typically not adjustable like a regular one would be... for good reason! I dive and fly RC as well & would have to suggest a small compressor instead of a scuba tank if possible for you. A lot of dive shops are sorta funny about filling tanks if you aren't certified to dive. Anyway, if scuba is the only way, the primary reg for scuba sits on the tank & has both hi and low pressure ports; you could likely use the output of one of these ports as the input to a more familiar adjustable reg. Your dive shop could likely tailor the output pressure to your liking. The tank pressure is 3000 psi so I'd stick with the scuba reg on the tank as it's proven, relatively cheap compared to anything else, and fits the sorta funky neck on the usual tank.