You should consider partnering with (or contracting out) to someone already well familiar with OS X and interested in writing a GUI.
Tarsnap has one of the technically best back-end implementations available, but the barrier to entry for an interested customer is incredibly high -- not just on OS X, but on UNIX as well.
Even on UNIX, producing a working backup setup requires writing custom scripts to do so, and implementing anything like snapshot-based backups is complicated enough that even I spent a couple hours getting everything working/tested, and I'm very familiar with this area.
I'll be bold: You solved the backup problem, now the number one hinderance to your growth is solving the user experience problem.
The UNIX utility should have an exceptionally easy way to configure backup schedules. Possibly even an optional web UI.
A Mac release must have a native OS X GUI (no qt!), be easy to use/configure, and be well-integrated into system services.
After the first iteration on the above you should consider implementing support for network-based backup administration, so that we can control backups/restores across all of our desktop/server installations from a centralized administration console.
If the above is not your forte -- if you're only interested in the crypto and backup issues -- then you need to find a parter or contractor who can step in and solve them for you.