In order to get to level 20, it takes exactly 65 wins (no losses) against a level 1.
From levels 1-10 or 12ish, you can get 139 pts per match (Win = 100, 3x Perfect = 30, 3x First Attack = 9). That is doing a Perfect round without a Ring Out (Ring Outs negate the points from a Perfect). That translates to 3 or 4 matches per level up to that point. 2 or 3 matches to get to the full exp for that level, then another match to hit you to the next level. When you level up, you should be halfway to the next level.
Once you reach level 10 or 12ish, your points per win go down to 119 per win, due to fighting someone well below your current level. You get 80 pts for the Win rather than 100.
Like Rogotogo, I used two copies of the game + two consoles to do it myself. It takes a few hours to do and is quite boring.
Also, you do NOT get experience points by doing Player Matches. These all have to be done in Ranked play.