Piecemeal updating to Catalina

I am hesitant to update my main computer to Catalina due to having to find a lot of replacement 64 bit programs at this time, but I would like to consider updating my work Mac, and some iPads for testing the new system when it reaches 1.0 + 10days or so. Is it reasonable to update a few machines and iPhones/iPads, or will I cut myself off from FileSharing on the iPad or being able to get my movies from a Mojave Mac to a Catalina iPad? I do not want to dive in with everything, but I have a few devices and would like to test out the waters, when the temperature is comfortable.

Anyone running the beta that can tell me if this would be a problem or it the new OS designed to mix well with older OS’s?

It’s really too soon to predict how things will be in the Fall, and even then, there will surely be glitches that need additional work. And that assumes everything that works for most users will work for you. Some of the things you mentioned don’t work properly for me today with up to date Mojave and iOS 12 platforms.