The amount of BB will be determined by the Bio-load. To ensure your BB has enough room for them to colonize, having media with tons of surface area helps.
Just add stock and let nature do the rest. A pre-filter sponge I think's a great idea ... can't hurt ... just more surface for BB to colonize.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.