ok - I don't see a problem moving servers.
Good question about the 301's though. Are there still many incoming links to the old URL's?
I think both of your models will work - I think I would go for:
point URL1 to URL2 then link URL2 to URL3
URL1 probably don't have many incoming links anyway and the authority of that URL is passed on to URL2.
I think the fastest way to move your URL's would be chainlinking - if you are lucky you won't even notice the change
BTW - why do you want to change your URL structure?