I think maybe the simplest way to start is to put it back up as a version 4.5. you have already the aolserver config file and either the database or a dump of it (latter case, just restore it), start it up and then fix any problems that come up.
As far as styling, the web designer needs to be made aware of the templating system and some additional tags available for the purpose of taking data from data sources and rendering it.
For the tags, look at http://your.server/doc/acs-templating and look at the designer guide.
If you wish to upgrade to the latest version of openacs, I would do this -far- away from the production server, maybe on a machine at home. You could either:
Last time I did something like this, I used the second method.
Whenever I back up, I keep two things: (1) the complete set of files that is the service (incl. the aolserver config file and if applicable the "run" file that daemontools uses, and (2) the database dump file.