RobW,
Yes, if you do the upgrade on top of 10.2.xx all of the settings are maintained. If you choose the option to " archive and install" your preference settings,3rd party apps., emails etc. are transfered to the new system. Any thing that does not get transfered is placed into a folder that's labeled "previous system folder" which can be deleted once you determine that all is well with the 10.3 install.