Franken-bass-tar thing I wanna build

[gunslinger_burrito]

I've always liked the idea of making a unique instrument, and without totally ripping off what Gentry Densley does, I would like to do something similar. The basic idea is to have an instrument stringed so that the low two strings are tuned one octave (or two?) lower than the higher four. I want my low chords to sound BIG. I think that I want just the low two strings, instead of three, to be tuned in this way so that I can get a little more articulation out of the "higher" end. I'm just not sure what the better options are when it comes to the techy-stuff.

Sooooo:

-I was thinking a Warmoth baritone neck (28 5/8")
-Offset kind of body, probably, unless I find a cooler one
-maybe two p-rail pickups unless y'all got a better, more fitting idea
-I'm aiming to be able to tune it (low to high): Bb (octave lower), F (octave lower), Bb, Eb, G, C

One big question I have is about the pickups. If I want to tune the lower strings down an octave or two, do I absolutely need a bass pickup? I'm not too savvy with bass stuff, and I don't know. That would require stereo outs, extra routing, etc..... so....Thoughts?

Then other question may just be of preference in sound/tone. Better or worse to tune the low strings one octave or two lower?

[IEatCats]

If you have a high output enough pickup, you won't need a bass pickup, but it will sound muddy unless the string gauge is such that it's a relatively tight string. At least in my experience.