Probably the max Bn you could put in your tank (adults) would be 1 for every 5 gallons/20 liters. Ratio could be 2 or 3 females to 1 male (only 1 male would be dominant).
Multiple males per tank would require 1 cave per male, and best to keep them from being able to see each other while in their caves.
As for how much wood is required depends on the size of the log imo(I give my bn plenty)
I keep my breeding pair (very prolific) in 33g 3ft tank. They are the only fish in the tank, but could be kept in a 10g. My pair produce 100 fry/month, which are moved to a 55g 4ft each month before the next batch comes out of the cave to grow out to saleable size... approx 3 months. Also I remove eggs every 3rd spawn to prevent overcrowding.
Here is a recent pic of my breeding tank. 33g 3ft (1 male and 1 female Abn)
grow out tank 4ft 55g which I limit to 200 fry
and project/back up tank 3ft 33g which houses 1 sf abn male, 2 juvie lf abn males, and 6 juvie albino/common X(all common)