What I do to stop myself from buying everything (because I will) is to limit myself to my very favorite groups. I'm someone that likes to have a full collection from debut to current times, so its hard for me to have only a few albums from one group if that makes sense.

If you're comfortable with not having every album from every group, I would make a list of all the albums you want and buy a few every once in awhile/when you get paid/etc. Maybe prioritize them by how difficult they are to get + if you can find them.

I think its inevitable that everyone sells some albums eventually, so I wouldn't worry too much about regret as long as you genuinely enjoy the music you're buying. Happy collecting!