My knowledge is incomplete as to what powers and restrictions you get with an amateur license, but I think the only real reason you’d want to use HAM mode in the US is if you wanted to operate on US 433 or maybe the 868 MHz block. Not sure if HAMs have access to the latter one or not, though. The 915 block is pretty permissive here for unlicensed use, so that’s usually sufficient.
Also, if a node is operating in HAM mode, it may not be able to mesh with other nodes not in HAM mode due to encryption being disabled. I could be wrong about that as I haven’t read into that specifically, but to my knowledge it tracks.





It’s theoretically possible but probably not practical.
There is a maximum hop count of 7 which means there can be, at absolute maximum, seven nodes between the sender and recipient. The default, though, is 3 hops.
While the radios may, in theory, be able to work at the range of “a few states over” as the crow flies, terrain, structures, and line of sight would likely prohibit them from working in practice at such distances. You’d also need a reliable series of hops to reach from you to them. Again, at those distances, you’d very likely exceed the maximum hop count pretty quickly.
From what I’ve seen, large meshes are generally regional.
There’s a way to join meshes over the internet via MQTT but I haven’t messed with setting that up and in some cases it can potentially overwhelm a local mesh.