Can Southern Wholesale deliver unassembled pallets?

Yes, it may infact be better to ship pallets unassembled because it reduces the freight cost.

What is normal lead time?

New customers or new products should expect a 2 week or sooner lead time, while existing customers and products will be filled from pre-made inventory and should be delivered in a day or two.

How do I figure BF (board feet)? How is BF used?

(thickness x width x length) / 12 = BF
Most lumber products are quoted "by the thousand" (i.e. $250/MBF).
BF x MBF = per piece price

2" x 4" x 8' = 64
64 / 12 = 5.333 BF (in a 2" x 4" x 8')

2 x 4 x 8 = $250/MBF
5.333 x .250 = $1.33 each