Challenges don't come from the system - they come from players challenging you specifically. The limit you've set will prevent any new challenges coming in ... ONCE YOU'VE REACHED 66 games in progress.
If you click on Open Seeks, you'll see the list of people (within the rating range limits if you've set them) looking for random opponents. You have to accept these challenges individually.
You can create any number of such challenges ... one at a time.
Joining a tournament is the easiest way of starting multiple games at once. Depending on the group size, you could find up to 22 games will start simultaneously. (As a basic member, you're limited to one non-official tournament at a time - so choose carefully.) You can join as many official tournaments as you like; a batch of these tend to start every month.
Do I need to start each one manually? Don't see any other way to do it. "Online settings doesn't seem to be starting new games though I've set it to 66 and open for challenges. What gives?