I do not consider it safe to draft closely at night, but if you are consider using your 2W low beam. Drafting using a bright light creates nasty shadows directly in front of the lead rider. BMB is a lot smaller than PBP so you cannot count on joining a group. If BMB leaves at 10PM it should be possible to ride with someone for the first night, even if your plans for the ride are quite different. I used a pair of LED tail lamps.
Redundancy is a good thing.
I used two home brew battery packs. One holds 5 'D' Cells. A set of 5 4AH nicads run the 6W light for about 4 hours. I like this setup because I can used alkaline 'D' cells, available at any 7-11 if I have battery trouble. Two of my friends use alkaline 'D' cells as their primary set, I tried this on the 600K and did not like it.