One hopping TRX per cell would ideally require 10 frequencies in the MA-List.
In the worst case, 9 frequencies, with very agressive downtilts.
6 frequencies are way too low, unless you push voice traffic on the BCCH TRX preferentially, so that you ensure that “hopping” TRXs are never all loaded at the same time (within a certain area). Difficult to ensure that, isn’t it ? So go for MA list = 10 frequencies (or even 11 if you can !).
Adjacent HSN are not an issue. Just ensure your MAIO in the hopping TRXs of one BTS are set to 0, 2, 4.