If it were me, as much as I love Black Limba as a tonewood, the amount of "warm" sounding woods you have already will give you a really warm sounding guitar with Limba. I would choose Swamp Ash, but then again, that's just me. It depends also on what kind of music you will predominantly be playing on it. If you were going for a Stoner / Desert Rock / Sludge sound then the Limba. If you were going for a more biting rock guitar, maybe for playing technical metal where you need that bite and definition, then Swamp Ash.
I have a feeling, though, that if you wanted to play Doom / Sludge / Stoner, you wouldn't be getting a custom made just for that. A beasting (and much cheaper than getting a custom) SG would be more towards that kind of sound. :D
Tell us a bit more about what you want out of the guitar, and some of the proper techies will give you a hand. The above is just my personal opinion.
*Reading back*
Although you do have a fair amount of Ebony going on in there... how thick are you having the Ebony stringers on the neck?
[Edit] Actually, tell us also more about the build, is it Neck-Thru or Bolt on or other, how thick is the Koa top going to be, what scale length, what kind of trem or are you going for fixed bridge, is it going to be string-thru-body etc etc etc. All this adds up and can greatly affect the opinions you'll be getting.
