All paid scripts would be included if they're transferable, but that shouldn't be a problem for ATX and ST. Most sites actually use free scripts, but that can be easily upgraded/downgraded
Moving to a new server wouldn't be a problem either, I've already done that a few times myself and have written myself a pretty neat "how to" to do that without or with very limited downtime. Basically all existing files can be transferred directly to your server through a .tar file and with wget. The Gallery database is a simply MySQL file that can be exported and imported into your ST-Database and the trades for AT3/ATX are stored in separate files that could be transferred too.
