Controlling everything just using volumes can potentially cause some issues. It would all have to be wired JB style with independent volumes, but that can/will lead to some loss of highs through the volumes to ground and other tone changes (particularly on the guitar side). Treble bleed mods are a no-go too due to the way the volumes are wired. You could wire it this way but I'm not sure the results would be ideal. I'd try to keep the two neck circuits separate.

You could do something like this:

Bass Neck volume (JB wiring) <--- Bass Neck pickup
|
v
Bass Bridge volume (JB wiring) <--- Bass Bridge pickup
|
v
On/Off/On neck selector toggle ------> Master Tone (0.047uF cap) ------> Output Jack
^
|
Guitar Master volume (optional treble bleed)
^
|
Guitar pickup selector toggle <--- Guitar Neck pickup
^
|
Guitar Bridge pickup

That would let you control the bass just using the volumes but have a toggle for the pups on the guitar. A Dano On/Off/On toggle would work for the neck selector. You would have to use the same cap on the master tone for both necks, but you could have 250K volumes for the bass and use 500K volume for the guitar and master tone. And, you get to stick with just the two toggle switches.

There will always need to be some compromises with a hybrid build like this kit.