Welcome and congrats all around!
I’m one of the type that likes to have my security system be just a security system, so I don’t combine mine with other Hubitat automation, however if you prefer then I would suggest the best contact sensors you can afford and repeaters. to make sure your Zigbee network is stable. NYCE contact sensors and motion sensors would be my recommendation for something as critical as that.
Otherwise, look at either Ring or Abode stand-alone alarm systems. Abode already has lots of integration options available and Ring has potential (more potential and Abode to be locally controlled actually).
For the locks, man that's a highly debated topic. I see a lot of complaints about Schlage, and I also see a lot of praise. Really seems to be the type, model and communication technology for the particular type and model.
Kevo is WiFi bridge isn't it? You're going to need to go to the cloud with that. I do this for my August lock. I use Google Assistant Relay to silently control it from Hubitat and I use a virtual lock in HE that uses IFTTT to update the lock status. WiFi bridges suck.
I have Yale YRD256 Z-Wave Plus on my front door. Love it, but some have not had good luck with the Z-Wave Plus module like I have and prefer the Zigbee radio module. Great lock either way though.
[Update] I now own a Ring Alarm system and use this excellent community integration with it.
