Welcome!
My suggestion would be to take your time buying your equipment. Rent your gear for a period of time to test what works for you. When buying your regulator, make sure it can be serviced locally where you live so you don't have the added expense of mailing it off somewhere, plus you don't know the quality of workmanship you're getting.
Don't bother buying a used regulator. You don't know its service history and how well it was taken care of by the former owner(s). Give serious consideration to using an AI transmitter. As
@SeanDavid702 mentioned, it's an added failure point and really just a toy to add on. I've been on many boats where a diver's transmitter has failed to connect.
Don't buy any Aqua Lung products, at least for now. They've had financial problems for several years, and they were just purchased again at the end of June 2025. I needed a replacement weight pocket and my local dive shops have none and Aqua Lung has none in stock and all production of new goods are suspended. As much as I'd like to support my local shops, it's not possible in this instance. I eventually found one on Amazon.