Hi Mike,
Hope you and your family/friends are all ok after the attacks in London today....
As for your question, I believe that Broadway Limited locos will work fine on 8 functions. unless you have *lots* of lighting or sound effects, I can't think of why you would need more. These are the function controls on my Digitrax Zephyr that I use with my steamers:
F0 - headlight
F1 - bell
F2 - whistle (horn)
F3 - coupler sound
F4 -
F5 -
F6 -
F7 - dim light
F8 - mute
F4 - F6 are all free (plus F3, as I do not have a decoder with a coupler sound on it). That should give you lots of room.
When in doubt though, check with Broadway... Good luck!
Andrew