Definitely have FFS before hair transplant. With hairline incision some of the M shape can be reduced, you might need 30% or even 50% less grafts. Compare that with possibly losing half of hair transplant because of doing it prior FFS.
You can do trachea shave along with other FFS procedures (safety depends on who is doing it) ... but if you are shure you will get VFS, it might be better idea to do trachea shave at the same time. Trachea shave, when done correctly, shouldn't effect voice in any way (after couple months).
Whether to do VFS or FFS first, it is completely up to your priorities. If your voice is really un-passable, keep in mind that your face might come-out very passable after FFS, and that could bring quite some attention.