My 2 cents...I moved everything over from ST to HE during one weekend. Didn't want to deal w/a declining mesh on ST and a growing mesh on HE and the potential associated family "why isn't X working" issues.
I did Z-wave first, and then Zigbee, IIRC, and as you've noted, working out from the hub.
I did my Z-Wave locks last, as they are generally the pickiest about a strong mesh and will want a beaming repeater (or two) like light switches near them.
Just prepare yourself and family members, if any, for a period where things are in transition.
Tons of helpful people here, let us know if you run into any issues.