There seem to be far too many issues with migrating and we're not in any hurry.
So... I thought what if I create a new site, new database, different domain - slowly start transfering/re-building our site in 1.5 on this new site. Then, once it's complete I point the original domain to the new site, change the configuration file to the new domain (remove the temp domain) and then install the SEF component last.
GollumX states, "Start by creating your own Joomla Installer." I assume I can use one of Rocket Theme's RTs, if I'm changing the look of my new site, correct?