Before buying anything you should visit the tracks that are closest to you and get a feel for the people and the atmosphere. Some tracks may have rentals and that would be worthwhile trying. You mention the 206 class and that is a great entry point for anyone. If rentals aren’t an option hanging around the track and befriending someone that is of similar size to you might also earn you a few laps, especially if someone is looking to sell their kart. The internet can be a good source of used karts and parts but you would be better off buying from someone face to face.
I thought there was a track near Boston, but heard that may have closed. Elias is in NH and could speak more to the location, but there are two tracks they race on with the NHKA.
Like a lot of “toys” there are some considerations. Usually, a kart has to be transported or a garage at the track can be rented if available. Do you have a way to transport a kart? I have seen people fit a kart into a hatchback or station wagon, but a van or truck would be better. A small open bed trailer is an option or even better is an enclosed trailer. You will need tools ( I have a dedicated set of kart tools that go with the karts) and once you buy a kart you will want spares for things that may need to be replaced at the track (axles, spindles, extra nuts and bolts, steering shaft, wheels).
Elias can also speak to the option of a tent program where you basically rent the kart, mechanic and storage. It might be an option to get started too.
Karting is fun and is likely the least expensive way to race something you sit in. Welcome!