How to configure Time Capsule etc as a local network server with remote access server and for backups

Question

I'm trying to set up new 3TB Time Capsule as a wireless network server (with remote access) and for backups for use in a small office (of two Macs). We have a late 2011 Intel MBP and a brand new MBA both running 10.8.3. We have two external 1TB hard drives that until now have been attached the MBP for storage and backing up that computer, which up until now was the only machine in use. The MBA is for a new employee and we need to share and work on the same files, both here in the office and ideally remotely too via Back to my Mac. The MBP needs constant access. The MBA only occasional. The TC has 7.6.3 firmware and we've set it up using AirPort Utility 6.2. It is currently attached to the MBP via ethernet and it has internet access via a Sagemcom router attached to TC's WAN port.
We've managed to set up a wireless network and both have wireless internet access through the TC
But there are so many issues I don't know where to begin - so I'll start with a description of what we're trying to achieve:
I planned to use the TC as the main server drive and place all the key folders and files there so that both of us can access them wirelessly and remotely. The MBP would back up to the TC and to one or two of the external hard drives - one being attached to the Mac via USB and the other being attached to the TC's USB port. We would back up the important data on the TC using SuperDuper and copy it to both external USB drives.
So , first of all, is that a sensible configuration? Should the 'server' be the one of the external hard drives attached to the TC USB port, backed up regularly to the TC using SuperDuper?

Answer 1

But when you say 'So using USB drive does make sense if you want to use it as a file store', do you mean a USB drive plugged into the TC? I hope that I can attach an external drive to the TC so we can all access and read/write the content wirelessly via the TC network or remotely.
Yes, USB.. as it prevents the sparsebundle mixing with data files. I guess it does depend on how much data you are talking about.. you can use the TC internal disk if you are careful and setup the sparsebundle with fixed sizes once you create them..
And to be clear, I wasn't planning on backing up remotely via BTMM - only to access the shared folders on the TC data drive or USB external drive attached to it. I'm assuming that's ok?
Yes, that is fine. Sorry I got the impression you were going to do backup over internet.
What is the alternative? Having a Mac Mini that's always on? Do I need OS X Server etc.?
A mini would be great.. you don't need server edition.. but I would see how the TC goes.. since you have it and it is much lower power consumption device. It is just that its design is not really for file storage.
One big problem I have is to do with the sharing permissions. For everything on the TC or attached external drive attached to it, it says I have only custom access and every time I try to change permissions it says I don't have the permission to do that. And if I try to change the owner it says my user name is not valid.
How is the security setup on the TC?
The security is a bit tricky.. I must admit since I run windows computer in the network, that I simply turn on the guest account to read and write access. For a business setup that might not be adequate  but it allows me full access to all the files.
If you setup the TC with user accounts then you are in trouble. That makes it very difficult to access, especially if one person already has the file open you may find a second user cannot login. I am not sure as I have avoided the security. IMHO it is meaningless.. since anyone with physical access to the TC can press the reset for one second and has full access.. and can add or change passwords.