I have a Decker with Full Cyberarm - nothing too surprising there. I'd like to switch to a modular arm, so I can muck around with having a lower arm for medic duties, for hardware work, or for runs. It's clearly a little pointless, but it has style.
Are my rule interpretations reasonable ?
Start with Full Obvious Arm - 1 essence, 15 capacity.
Bulk up with +4 Bulk rating - now 1 essence, 19 capacity.
Modular Partial Arm - takes 10 capacity, makes 8 free in arm, no essence change as it's replacing cyber? - now 1 essence, 9 capacity in upper arm, 8 in lower arm.
Transfer max 2 bulk rating from full arm to lower arm - now 1 essence, 7 capacity in upper arm, 10 in lower arm.
Can now get multiple modular bulk 2 lower arms and fit 10 capacity stuff like medkit and toolkit (or cyberdeck+1 armour+large smuggling compartment) in them, with +3 agil, +2 str, +2 armour in the upper arm, at a cost of 13000 per lower arm plus contents.
Of course, it's still a lot more expensive than just a bulked up full obvious arm and a medkit/toolkit bag, with no mechanical advantage.