Wow...where to start? The Sansamp Flyrig5 emulates several tweed amps, the plexi section adds the classic Brit Plexi overdrive as well, also it incorporates a delay and a reverb. The Bass Flyrig is based on the VT circuit giving the B15/SVT emulation, plus a tuner, compressor, and other useful things. The idea is to run bass freqs in channel A full range and guitar freqs through channel B full range. This shouldn't be a problem as the Pog2 won't pass bass frequencies to channel A when it is set to 'octave up'. This should be like having a bass and a guitar on 2 seperate amps.
My reasoning for using the 1855 for bass and the TC for guitar: the 1855 has a built in dip where guitar frequencies have a natural peak, the TC is clean and even throughout its range so in my mind better suited, of the two, to handle guitar frequencies. Further, I need more power to push bass frequencies than guitar frequencies which is why I am looking at 4ohms for the 1855 and 8ohms for the TC. If I were to recombine the signals I would just use a mixer and two PA speakers (what I use currently and may end up continuing to use if my experiment flops).
On the 10: I have commissioned the build based off using a pawn shop bass and string pairings for the tuning listed, I have not yet had a full complement of all ten on one instrument. So far, I haven't noticed anything too weird as far as harmonics. If it doesn't pan out I can simple go to straight octave tuning no harm. The idea for the 10 came from the desire to play in bass/drum duos and power trios. In those type of arrangements there is a lot of sonic space.
I don't think I want a hybrid cab. If this doesn't work out the 1855 and the TC both have excellent value, a hybrid maybe not so much.
I hope this clarifies what my thinking is. I realize this is a little outside the norm but I like to play around with stuff.

Rondo