I play progressive metal stuff in drop B, BF#BE, so similar but not the same.
A lot of it is down to personal preference. I use a .125 on the B as if I go any heavier, I find it comes too dubby and loses high end harmonic content. I doubt id change it for A#, as the tension is very similar. Couple of bass set up tips; Get the neck as straight as it can be, even a tiny bit less relief will really help. When stringing up a new A#, when you know where the string will break over the bridge saddle, take the string off and bend it slightly at that point. The thicker the string, the more this helps get a clearer low string.
I personally wouldn't go to 105 for a F, I use a .95 for an F# and would think .100 would be fine. As long as you're using some compression, which I'd definitely recommend, you don't need to worry too much about balancing things out.
I do keep lows clean, I think my crossover is somewhere around 120hz off memory, but again this is to taste. Difficult to do with the gear you use, and can't really be duplicated with EQ'ing. Considered swapping that B3K out for a Darkglass X? It'll be a big upgrade and will allow that crossover.
Forget about FoH, the sound engineer would rather just use his tricks than undo yours first.