Seed sowing density and tray size?

Just wondering what are the recomended densities for planting various sp and also what can i use for planting large numbers of seed? PIcs would be great if anyone has them.

This is what it says on the back of my big brand named cactus mix seed packet:

SOW: Scater lightly in pots or trays of seed raising mix, firm down and moisten, keep in warm place. Some seeds may take months to germinate.

CARE: Can be potted individually when large enough to handle (carefully) but most spectacular when grown together in a large container. Like all plants, cactus benefit from applications of a big brand soluble fertiliser. Protect from snails.

That's word for word...

Other than Sow late winter to early summer (subtropical to tropical region), depth 2-3mm, germination 4 - 12 weeks, plant space - enmasse.

Personally I don't know if that has helped - it's for various species that's all I can tell you.

Pictured on the front are various mammaliria, opuntia, even astros! But god only knows what is in the 0.2g (approx) of seed!