I have been running HA on a Pi3b for a few years. It's been a bit flakey the last few months so I'm looking to upgrade to a Pi5. After the replacement I expect to add more items and maybe phase out the Insteon for more Z-Wave.

I plan to "start from scratch". I use an Insteon hub for most switches and 2 garage doors, some Z-Wave switches, a few generic lamp plugs, 2 cheap Matter bulbs, and Alexa for my wife. Maybe 20 devices or so. The only automations are 2 sunset items and one that links a Z-Wave switch to a insteon switchlink. What will be my major pain points for rebuilding?

Or is there a straightforward method to migrate directly?

What kind of problem will this be for my Nabu Casa subscription? Alexa integration?

Or do I try to build first, then decomm the old one? Won't that cause a conflict?