You say you are going to do research and that is the best thing you can do. I’d start with the bike you have now. Since you bought your first bike in 15 years a few months ago and how you want to build a bike, that one sure missed the mark.
You should still be in the best thing I did stage or just leaving it if you really liked the bike. Even then a lot of people who love their bike will look to upgrade it first. So figure out what you wish you had bought.
You may also want to test out other bikes that you may want to buy complete instead of building as it probably will cost more to build. I’ve built bikes and it is a lot of fun, but don’t plan to have everything fit perfectly. That only happens if you transfer from basically the same frame. You will end up with parts that don’t work.
John