The conversion tool does not copy over any custom stuff.
I also found that some misc applications/destinations were disabled.
All Trunks are disabled.
See here how copy some stuff that is not being copied over with the tool: How to: Upgrade FreePBX13 to FreePBX14 on Hyper V - Guide
As far as the cutover, I’d just change IPs, so in case something is badly wrong on the new PBX you can just switch back
