Which software would you recommend to do the first stage to? I'm looking to try and keep as much as possible to do less manual work later. So a format that keeps permissions etc would be highly preferable!
ocPortal seems to be a CMS. Getting an importer for it won't be common. Maybe a bit easier to find with an open-source project that's been going for a while (phpBB would be an example). I'd assume you'd have more luck making your own though.
Edit: It's not very popular. I can't find any importers for it at all, at least for a two stage import. It'd probably take more than two stages, and possible data loss. Very likely you'd have to make your own importer though, so I'd just do that. Save time and money.