integrating members from another database into IPB--SORTING them

[raincat]

I currently have a site that has evolved into quite the mess.  It has about 85,000 members, but most of their details exist in two databases* other than IPB (but not other forum software listed on the migration page) . . . but the site ALSO features an IPB with some duplication/overlap.  

And was wondering how I could/should move forward with all that in the future less confusingly, probably continue in some fashion with the newest version of IPB, but also hopefully get everyone under one member database "umbrella," and then wondering . . . could I actually just get IPB to do everything I need to do here?

It would really be awesome if I could.

And I'm imagining it's probably possible that I could IN THEORY, but I have no idea what would be required to get from here to there.  And I'm imagining it might be difficult.  And I'm hoping for some large hints.

I'd have to do 2 main things, the first is in another thread, the second being that I'd need some way to do a fairly complicated selective display of something like a Member List.  I don't know if it would actually be something with the actual Member List in IPB, or . . . something else?  It seems like it would make the most sense if it were the actual member list, but I don't know what's actually possible here.

I did a lot of searches, and if there is a product in the Marketplace that would assist me, I wasn't able to understand that that was the case.  I also read all the documentation I could find on Pages, and I'm still not sure if that might work either.  I haven't yet upgraded to the current version of IPB.**

But basically I would need a way to do a sort that would be like you'd imagine for a personals site.  Like, some custom fields/exclusion criteria in one member's profile could be compared to those of other members, such that only a smaller subset of the entire list of members would be displayed for each member that was logged in, only their "matching" members.  

A sort, of sorts, but much more complicated than just something like sort by date joined, that's the only criteria, etc.  A member list, but only containing a smaller subset of the whole, just for them, based on their criteria and their profile.

If it wouldn't be something with the Member List itself or Pages, I'd love to find SOME way to do this within IPB.  Any suggestions would be great.

*Left out most details here, imagining not relevant.  If some actually were I'm happy to provide.

**You might imagine I should just upgrade to the current version, then find out by trying out Pages then.  That might be the case, but I wasn't sure.  I thought this might be a situation like it can be with upgrading your computer's operating system, how it might be helpful to know what apps you're going to need in advance, so I thought maybe asking some questions before trying to upgrade would be the more clever way to go here?