That doesn't look so bad at all. The BFD should be able to handle it fine. BUT, REW will most likely reveal more problem areas to deal with.
Measure your sub only because we can't do anything with your mains via the BFD. Let's see exactly what the BFD will deal with. Don't worry about getting to 80db at 100hz... that's probably above your x-over point anyway, which should most likely be 80hz or less. Just use the same level you just used and measure... where ever 100hz comes in.. it comes in... this is what you want to know.
