Congrats on your new hobby, and welcome to Scuba Board.
Where do you intend to dive? If it's mostly in FL / Caribbean, you should know that flying with a tank is a major PITA, versus renting on-site which is easy and cheap. Most people rent when they fly, unless they have a really good reason to use their own tanks.
If you intend to dive a lot within driving distance of your home, then buying some tanks might be worthwhile. It will take a few dives to pay for itself, but you'll get there eventually. Understand that on top of the upfront cost, there is an annual inspection of approx $20/tank, and every 5 years you'll need a hydro test for maybe $50/tank. For those reasons, I say that the main upside of owning your own tank isn't the savings, but the freedom to fill it whenever is convenient, rather than planning your dive day around pick-up/drop-off.
I have never dived on the East Coast. But googling it, the temps look similar to the West Coast. Here, most people dive steel tanks since (1), they contain more gas for the same weight, and (2) they take up less volume for the same weight, meaning that you can take less lead. I think you'll most likely be happier buying steel tanks. Assuming that your LDS can do high-pressure fills (that is around 3442 psi), go for high-pressure instead of low- or medium-pressure tanks (2200 - 3000 psi).
Steel tanks pretty much never go bad, unless they rust. The inside gets rusty if the tank is stored empty, and the outside gets rusty when salt water gets trapped against the tank without being properly rinsed, like under a rubber boot. Buying used on FB Marketplace or Craigslist will probably save you $100-200 per tank. If you go this route, I would recommend convincing the seller to let you drain the tank, remove the valve, and see if there is rust inside. Make the sale contingent on there being no rust, if there's any rust inside, don't buy it. Seller should be confident enough on their maintenance to take you up on this. After you drain the tank, you'll need to get a new visual inspection from the local dive shop for about $20, which often includes the first air fill.
Whether they let you take the valve off or not, definitely remove any rubber boot or netting from the outside of the tank, and inspect for exterior rust. I would accept a tiny bit of rust coloration on the outside, but refuse anything with a pit deeper than the thickness of my fingernail.
