As always for CSSU you should follow the instructions on the wiki page for your flavour of choice.
https://wiki.maemo.org/Community_SSU

You should be on PR1.3 or 1.3.1 first and you will need the nokia repos working to install system updates, aka 20.2010.36-2 or later

If your system is ready as above it's as simple as following the one click for your flavour from the wiki in the N900 browser.

You should use the default application manager for all updates.
I certainly have no idea where installing the metapackage with apt was advised.

Perfect Setup wiki page was a nice idea but is all opinion and pieces of wiki pages smashed together so see caveat at the top of its page.

If you need more back and forth advice and you are struggling with the wikis etc, there are plenty of helpful folk on #maemo IRC freenode.