In my limited knowledge and experience, there are broadly three versions of every tube, USA, European and Russian. Chinese I don’t trust except Shuguang which am yet to try.
6P1 aka 6AQ5 or EL90
6N1P is a bit similar to 6DJ8
However the tubes with less gain are suitable for no gain buffers. 12AX7 as I mentioned above is NOT but is the most popular tube used in preamps.
Don’t just go for a tube buffer which has cheap replacements. I have experienced 6J1P-ev and 6DJ8 Tube buffers and found latter much better.
For tube preamps, there is no limit of tubes and topology.