Zach,
I like what I see so far on your initial proposal.
In the past, I have been involved with 2-HOP and 3-HOP packet attempts using various combinations of the ISS, NO-44 and NO-84 when they were all working on 145.825MHz.
Your proposal of using a 9K6 FSK 2-port_digi's on board three satellites in the same orbital track resolves what I believe to be the main challenges we faced in our 1200 baud experiment. If the footprints overlap, the satellites should be able to talk to each other.
1) Since the satellites were in different orbits, there was Doppler shift in the signal between them. In your proposal, doppler is minimal for FM packet.
2) With your 2-port digi, the repeated packets between satellites will not be interfered with by multiple up link signals. Improving the success rate.
3) I find that 9K6_FSK is as easy to copy as 1200baud, so efficiency in channel usage is gained.
Once the operators acquire confidence in establishing basic 2 & 3 Hop packet contacts, the other experiments and distance records you mentioned will follow.
I'm in.....
BOB KO6TZ