The BLB bulbs emit enough UV to be useful - but they are much slower than BL bulbs. Their lower price makes them worth using to me.
I did not see any significant difference between aluminum foil and glossy white paint. YMMV.
I use the instant on. In another thread, Sandy King actually tested and found light intenisty varaiation in the first minute (IIRC) but little after that. In a typical exposure running several minutes, the amount of variation was insignificant for our photographic purposes. I've come to the same conclusion in practice with both salt prints and VDB.