Good approach. Remembering this is hub that runs groovy, not a reincarnation of the ST hub of days gone by will be serve you well. This is an excellent, stable platform if it has the right devices, drivers and apps.
I too am ex-ST, but no where near the number of devices you have, so not expecting a 100% conversion and compatibility, while looking at devices that might need retiring as you go would be my best advice, based on what I've seen from other users that have that number of products to move. Where expectations are not met seems to be when an unrealistic expectation that every product, no matter the age or how difficult it is now to pair or join seems to create a common misconception that Hubitat is somehow under performing.
These are good points to keep in mind. If you have been on ST for three years and have that many devices, then there's little chance you aren't a big webCoRE user. The port for that level of devices and use has been largely unsuccessful based on the feedback from other webCoRE users that have now converted to Rule Machine. In general, former ST users that have tried to move webCoRE and just carry on with their pistons on HE have discovered that their system will, if not at first, slow to a crawl or lock up. Remove webCoRE and the hub returns to it's normal speedy responses. Your best success will come from spending time converting or redesigning your automations to run the native Rule Machine.
As Homebridge goes, I will say that if you're not running iOS devices, its moot to even talk about it. If you are, then my experience is if I reboot the hub without shutting down Homebridge, it throws API errors on Homebridge and HE slows or even locks up. But if I simply stop Homebridge, reboot the hub, then restart Homebridge it's absolutely no problem. Not everyone has my same experience with the reboot, nor do they share my successes with running Homebridge at all.
Good luck. Ask lots of questions, but make few assumptions and you'll be quite happy with your decision I think