A "mini Exchange" is probably too much.  Do you really want Public Folders at home?  And are you going to schedule family events by creating a new Meeting Request?

I suspect HTTP mail (Hotmail) and SharePoint-like contacts/events are probably close to sufficient.  All three of these can (in theory) be run from a home box with IIS.  Somebody just has to reverse-engineer the protocols...or get Microsoft to document them...