Here's two format ideas for you
1) Home vs Home Format
** New players typically don't know that you can play rematches during the season. Also players who split their first two matches may play a third match to determine who is the regular season winner. So if you know you have a player in the league that you really like to play then just schedule two matches against that player, one at each player’s home court.
2) 4-person, 8 or more Round Robins
* In the Boston community we typically organize a Saturday or Sunday round robin between a bunch of players from the same skill level. We'll play two 10-game pro sets against each other and both matches will count in the standings. It's fun to get together in larger group setting and you might meet new players that you haven't played before.
** You need someone who will to take lead on organizing attendees, match-ups, location, start time and getting an even number to attend.
** No reason why 6, 10 or 16 players can't participate, you'll just need reliable access to enough tennis courts plus a competent organizer.
** We typically have the winners of the first match play each other and pair the non-winners in the 2nd matchup.
** Sometimes it's best keep a time limit for the first match to 1 hour and 15 mins.