Although I think you could 'get by' with 14 buttons, I don't agree that you'll get everything you need, not by a long, long way.
I can't be bothered to look up the names of all the things I bind since I use default keybindings anyway..

So I'll just list the buttons I use;
Need-or-Die;
6, 8, 4, 2, 7, 9(the joy and two of the shoulder buttons I guess would be most natural for these?), Z, Tab, \, Q, The Arrow keys(D-Pad?) Ctrl, Space,
Could probably live without having immediately available but would feel their loss;
D(Alt-D), home, delete, insert, end, page up, page down, ,, ., /, backspace, Y, H, V, B, T, N, E, K, scroll lock, shift-scroll lock, then all the AI commands (which I actually do the quick way using the shift-p, shift-e, etc combinations), F-Keys depending on how complex the mission is (read; hotkeys so as many as needed),
After about "B" They start to become a bit less likely to be used in a mission unless it's 'hard'.
That's what, 49 keys?
16 if you stick to the ones I listed as need-or-die, and that's before targeting or even weapon selection?
I am not satisfied with your xbox controller!