the 80mm and 90mm are going to mean how wide the ski brake is. For example a 80mm ski brake will fit skis with a waist width of less than 80mm. So you should look at your waist width of the ski you want to mount and buy a binding accordingly.As for your question about using the same brand... There is no reason to buy the same brand because all ski boots work with all bindings and all bindings (with the appropriate brake width) will work with all skis. Also, I would honestly recommend researching what would be good beginner gear, because you don't want to spend a whole bunch of money on stuff that you don't need. For example, In almost all cases beginners use a very very low DIN level on their bindings so the skis will come off very easily. So you wouldn't need to spend extra money on a high DIN rated binding when you would be fine with a cheaper one. Good luck finding gear, and keep asking questions!!!