I posted my breeding strategy for Tiger Barbs in
this thread. The strategy works for most barbs and small characins, and I have bred many species using that formula.
For Lemon Tetras, I would use soft water, ~3 degrees hardness, a pH of around 6.5 with the temperature around 25C/77F. Tetra fry are generally too small to take BS nauplii from the start, they will need cultured infusoria or a quality liquid fry food.
How many eggs depends on age/size/condition of the parents. A really full well conditioned adult female can produce a few hundred eggs, although typically only about half are viable and hatch. Deformities and other defects reduce the fry further, but from a good spawning, you could easily expect to raise 50-70 fish.
