Welcome. Like you, I got started with Homeseer back in the X10 days. I kept a Pi version running until a couple of years ago for a few things, even though I had switched to Insteon and the ISY for a couple of houses, and then Z-wave with ISY as the initial system in the current home property, before switching to Hubitat going on two years ago. Very happy with it! As others have said, don't try to move everything over all at once, in a weekend binge. More than other systems, I find letting the z-wave system figure things out slowly works well with Hubitat, as routes get figured out by the z-wave radio.
As for Rule Manager, it's not nearly as intuitive as Homeseer Events, but it is very powerful once you understand it. Just expect to experience a bit of a learning curve as that happens (another good reason to go slow on the switchover).
As for reboots, I have four hubs across four buildings (two properties) and in two years, I think I might have felt the need to do a reboot once in each of two hubs, and one of those was probably unnecessary. Only once has a hub just "locked up" and that seemed to be caused by a bad z-wave device that was spewing out traffic. When I left the ISY community (in a bit of a disgusted huff at the company and forum, not the device itself), I was afraid I'd miss the ISY's reliability, which was great. That hasn't happened at all! Hubitat has been rock solid for me, with not even a fraction of the reboots and problems I had with Homeseer. It seems to be on par with the ISY, which is saying a lot.
Finally, the community here is very helpful and reminds me of the old Homeseer forum of maybe the 2005-ish era in terms of helpfulness (really good). Dramatically better than the fan boy attitude one finds on many of these forums, although there's a little bit of that creeping in as the user base grows. Overall, I'm extremely happy that I made the switch, and hope you are, as well.
