Cachly does have basic URL scheme support:
cachly:// Opens the app
cachly://?gccode=<code> to open a specific cache
Adding more is for sure on our radar.
This will be all fixed in Cachly 2.1. There are major performance updates and we have tested an offline list with 50k caches that loads in 2 seconds.
Yes, clustering will be used when an offline list is a certain size, but will not be used if under that threshold. This will be a user definable setting.