OP, as someone a few weeks ahead of you getting into ‘this’ - that is to say, the hobby, and learning about these watches - my advice echoes others on here, that is to spend time researching and looking around. You can be methodical about this, and save yourself searches like ‘Vintage Omega Seamaster’ or ‘Vintage Omega Constellation’ which is what I started with.
Firstly, work out what references/case numbers and styles of watch you like, and then learn about what constitutes a good example. That way, you can narrow your search a lot better. I’ll say that for all that is said about Omega Enthusiast and his pricing, his videos on YouTube are an excellent resource for learning in sometimes encyclopaedic detail about these watches, and there are in particular some great videos on Seamaster references that break down similar styles and talk about the differences, what to look for etc.
Secondly and as others have said, once you know what you’re looking for, use the search function of the forum and search for titles only so you find threads that talk specifically about the watch style you’re after. You’ll also find threads of people asking ‘is this watch legit’ etc., and in their reasoning members will always explain why a watch isn’t a good example so you can learn. Also use this search to look at past listings in the sales section to find one at a good price.
Finally, I’d be very wary of dealers, unless you’re really sure of what you’re looking for. Almost always you’ll pay a big premium, but sometimes you pay that premium for a good example, in which case if you’re happy to do so then great - however 99% of the time perseverance will lend you to finding a similar or better example at a much cheaper price on here/eBay/auction etc.
Happy searching!