(1) You are limited to 20 created players ... so you can build 2 ten player teams (with 1 legend each)... save it as a season... load it whenever you want these 2 teams to play each other. You could build as many of these 2 team (20 created player) saves as you want, but only these 2 teams could play each other. If you don't mind building these team combinations to play against each other, you are fine. Once you save the 2 team combinations, you can reload them at will - but they can only play each other (or the games saved default teams).
(2) We know this works, obviously RateSports found a way to get more teams available to play each other. I don't know how to do that or if those teams can be edited.
If #1 will suffice you are good to go.
If #2 is what you are seeking, try to get in touch with RateSports. JYoung may also have more info/knowledge.