You raise great considerations, Rosie. I also consider a few others:
How easily can I host / manage the platform?
Can I “own” the data on the platform, or does a third-party own it?
Will I be able to “future-proof” this platform, and its community?
My community has existed for over 33 years, both online and offline, across various platforms and through numerous incarnations. So for me, longevity and control are key features that ensure that I can help guide, support, and nurture the community to my vision.
What does their release schedule and the release notes from the last year or two look like?
Asking these should help you work out if the platform is still a going concern for a vendor, if it’s just in maintenance mode or even if it’s being neglected entirely.