You can start with as little as 50. The females have the black "stem" protruding out the backside while the males only have the two antenna looking things coming out their butt.

I use vermiculite which I get at the garden center for the breeder bedding. I used an empty sour cream tub. They can lay eggs up to in inch into the soil, so be sure it's deeper than that. You can also put a screen over the soil so they lay the eggs between the grates in the screen and that way no other crickets will eat the eggs.

make sure after a while to take the bedding out so you don't have the pinheads with the adults. There are so many details to the process that I couldn't outline it all here. There are many guides online. Post any other questions here and I'll try and answer.

I also breed mealworms, working on my first colony now.