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The four modules you mention all work with XOOPS 2.3.x or have versions that do. No big deal for you there, just make sure that you have the right versions of the modules to hand so you can upgrade those too straightaway
However, it's the custom modules that you need to check out before upgrading. Can you install XOOPS 2.3.3RC on your local PC (using, say, xampp) and test the custom modules?
If the custom modules work then with just a few modules you have a few hours work at most.
However, do your homework first.
1. If you can get the xoops_lib and xoops_data folders out of document root (i.e. xoops_root) then do it that way from the start rather than try to move them later. Rename then from the start.
2. Make sure that you know how to install the Protector module at the time of installation. Follow the instructions with regard to the mainfile.dist.php file.
3. Make sure to know the database and user passwords (they are in mainfile.php).
The upgrading process is really rather straight-forward and I think you should do it yourself. You can always ask for help on here, of course.
you could then enhance the site with the PM and Profile modules (that ship with the core) and add a nicety or two, e.g.
Instant Zero's xoopscare module to keep the site running sweetly
Personal view:
If it were me I'd do my homework first and wait to upgrade directly to v2.3.3 which will be released very shortly - the bug-fixes for the PM and Profile modules are worth having and this will save you a further upgrade so soon after.