Great beginning sax lessons, please check out this playlist: https://www.youtube.com/playlist?list=PLWMjC05R8fbX92AKF4SIyXa5kNEdHa0m2

For a great secondhand sax, I recommend you go to a local saxophone repair/sales shop, preferably a small family-owned one. Not only will they be able to sell you a good second-hand sax: they’ll set it up for you, and make sure it plays well. I don’t know where you live, but this is the kind of store I’m talking about (they have brand new saxophones that are less than $1,000): https://www.brassandwinds.com/