Hi aj,
I'm by no means an expert, but I have struggled mightily with a few of your needs. First, certainly listen to Bob, above me, as he seems pretty expert at these issues. I've haunted his messages a few times to learn how to do things through the work of others.
I tried once to host an iTunes library on an Airport Extreme, and it doesn't work. The unit (and, I'm assuming, the TC as well) is just not set up as a file sharing device. You want to believe that it can do that, but I think it just can't... or does so so poorly that it's not worth the time you'll put into trying to get your connected devices to communicate with it properly.
Second, again keeping in mind I'm not a professional... I have really battled for a long time with the idea of two people (or more) working off different iLibraries, and I gave up early this year. What we have done and what has worked so far is connect our different devices to the same iCloud account. This has worked for us so far, and depending on the size of your music library, would save you the initial cost of a wireless HD if that's what you want to do--I say initial because presumably after a time you'll be paying annually in iCloud storage what you'd have paid once for a device.
This meets her need to access as much stuff as possible and not worry about it and my need to bring my OCD-level of crazy to the problem of "syncing" across devices. We have not had any issues so far.
Soon I'll be installing a new home system, though, with (ideally) the "home" libraries on a desktop iMac... this will keep the hard drive copies and the TC will keep the backups... Then, (again, ideally, I'm not sure how this will go), the other iDevices and Macbooks in the family will point towards that iCloud account, and things should work out.
I hope.
But the point of all that is I played the "This is my stuff, That is your stuff" game with my spouse for years and it never worked out. Having a merged iCloud account has done wonders.