I think OS X workstation will handle up to 10 connections from remote systems, so what about just getting a Mac Mini (even a G4 would be enough) and using that as the “server” out of the box? I wouldn’t normally use a laptop as a server, since there’s normally a fair chance it’ll be away from the house when I need it.

Unless I’m way off base, any OS X system should be able to serve files via Appletalk or SMB (for any Windows systems that ever happen along), and you should be able to set up some kind of wiki pretty easily, too. And I guess you could consolidate your iTunes content.

If you needed access to the content from off-site, you’d need to set up some port-forwarding rules in your home router (e.g., to send all inbound webserver traffic to the Mini), and then to make it easy to remember what address to use to contact your home server, you register an account with dyndns.org so that mjc.dyndns.org (or any other name you want under 88 different domains) will resolve back to your place.

That’s a fair amount of DIY, but it’s not ridiculous. You could also opt to get a web host somewhere else, and put the Wiki there.

I know John Gruber and his wife share shopping list type info with Tada Lists because it has an iPhone interface. This may be a little less than you’re after.

mwr’s recommendations are good. I would add that the path of least resistance to offsite access to stuff is the Back to my Mac feature from Apple’s .Mac service. Also, I have had good luck using DynDNS without port forwarding to access my Airport Disk over the WAN.

Another stupid simple way to do this would be to use a wiki like PBWiki or even a simple, private blog using Wordpress or something to leave a “what’s new” paper trail for each other. With Wordpress, you could each be authors, hide posts for people not logged in, and then subscribe to each other’s posts as an RSS feed that could then be munged however you need to whether it be to pipe it into email or to SMS.

The financial stuff might not be as easy. For me, my wife and I are joint account holders for our bank accounts with ING and we each get our own login info. Check with your bank to see if they have a provision for adding another user to an account.

Bills I would do with a calendar, probably with iCal or Google Calendar.* OS X Server now has CalDav built in, but you could use BusySync to have read-write access to the same calendar and keep it in sync.

I realize this post is sort of all over, but I hope I’ve given you some stuff to play around with and find a solution. I’d be interested to know where you land.

*Come to think of it, Google might be a good place to store some of the not-as-sensitive info. Google docs for lists (or even Backpack maybe?) and calendar for scheduling things.