ST-1JR ...but it may not end up that way.

[Muzza]

a) Also not sure peg head would be... ...strong enough.
c) cannot even think what guage bass strings you would need

Answer a) Not a problem as there will be much less tension than a regular tuned 6 string. Because of the shortened scale, you'd need to really loosen off the strings to get it down to E A D G tuning.

Answer B) I'd start with the biggest, thickest strings you can get. If they're too thin, they'll just flap around like over-cooked spaghetti.

I'm thinking a good place to start would be E - 0.130, A - 0.100, D - 0.080, G - 0.065. Basically a 5 string set without the 0.045 G string.