How to manage collections that are "too large to sync"?

I am in the process of "upgrading" from an Explorer + to a Mini 2.

Several of my previously generated collections will not sink due to being too large.

What are the size limitation for a collection on the Mini 2?

I am preparing for a 23 day rafting trip on the Colorado River through the Grand Canyon. My collection includes around 700 waypoints, and several long tracks from previous trips.

Do you have a suggestion as to how to parse an existing collection into multiple in order to meet the limitation?