The TC is built as a network target for Time Machine backups.. it is even more designed for TM backups of laptops by wireless.
Using it as a NAS.. is possible.. you are doing it.. and over wireless it is limited by wireless speed .. but from a NAS point of view it is slow.. ethernet speeds are way below full gigabit which even cheap end multi disk NAS are reaching.
The total lack of any sort of built in backup other than full archive.. which stops all use of the disk for as long as 24hours as it backs up the entire disk to a USB drive shows it was never intended for this usage.
If you want incremental backups, Carbon Copy Cloner can do it.. I did test SuperDuper a while ago and it could not manage network to network backups.. however it may have improved since then..You need a target disk.. I guess most people will be tempted to use USB drive plugged into the TC.. and that would be the worst possible location.. since you have to run CCC from a computer.. all files are dragged across the network.. then sent back again.. and even worse to the USB port which over network is super slow.. by wireless read super extra slow. as double handling packets over wireless is to avoided at all costs. It is much better to plug the same USB drive into the computer that CCC is running from.. !!
Or is there a better alternative configuration that would provide the redundancy we are looking for. Hooking up a RAID 1 NAS to the Time Capsule and having it serve off of that perhaps?
Plug a NAS into the TC and use that for file sharing is a great idea.. however.. RAID is not backup.. You need to still backup the files to a drive.. but any true NAS will do that automagically itself on suitable schedule you can set. You plug a USB drive into the NAS and it will do the backup.. in fact for a business.. I would do a few backups and swap the backup disk weekly to a different location.. so fire/theft would not cripple your business. The most you can lose is one week of data files.
NAS are not cheap.. It will basically cost you a computer. And that is what it is..
Top brands, Synology and QNAP are very Mac / Apple aware. Have excellent browser based admin.
Look at http://www.smallnetbuilder.com/tools/charts/nas/view
