Input Once, Output Multiple (or, "Am I on the right track?")

[Kieren Richard MacMillan]

Hey, y'all:

I'm planning the engraving of my first 'big' project in Lilypond, and 
want to make sure I'm headed in the right direction!  =)

It's a carol for choir and brass sextet, with a reduction/arrangement 
of the instrumental parts for piano and a separate one for organ. The 
choir has significant sections in "unison" (i.e., octaves, really), a 
fair bit of homophonic work, and some true counterpoint.

I need the following:
1. Full (conductor's rehearsal) score, with 4-stave SATB, 6-stave 
brass, and 2-stave piano reduction.
2. Choral score, with 1- to 4-stave SATB and instrumental reduction 
(piano).
3. Organ score, with 1- to 4-stave SATB and organ accompaniment.
4. Individual instrumental parts (6).

If it's not too much extra work, I would also like the following:
5. Reduced study/rehearsal score, with 1- to 2-stave SATB, 3-stave 
brass "compression", and 2-stave piano reduction.

I'm considering the following setup:

tptOne = ...
tptTwo = ...
horn = ...
trbOne = ...
trbTwo = ...
tuba = ...

choralUnisonA = ...
choralUnisonB = ...
...
sop = ... (all voices should/may reference choralUnison sections, with 
transposition/transformation as needed?!)
alto = ...
ten = ...
bass = ...

piano = ... (can I "implode" selected music automatically from the 
instrumental parts?)

organ = ... (as above)

From there, I think I can build the scores appropriately.

Questions:
a. Does this sound like the most feasible/viable option?
b. Is there a way that global contexts can be of assistance?
c. For sections where the instruments strictly double the voices, would 
it make any sense to "share" notes?

Thanks for any pointers,
Kieren.