if you go to the "Leagues" link from the main KCFDC.org page, you'll find all the info you need about leagues.
There is NO requirement to play open at Olathe league...or anywhere else.
Monday is the busiest league night---Cliff Drive, Olathe, and the New Player's League at Rosedale. Any of them are great ways to learn more about the game...but, just as important, show your support for what the Club has done, is doing, and will be doing by joining!
the KCFDC is responsible for all the public courses in this area (except the California Trail course). Anytime you play in the KC area, you're utilizing lots of hours by lots of volunteers from the Club who worked their tails off to design, install, and maintain that course. Every $$ helps a little more, and every warm body does too.