Doubling doubling doubling is there a limit?

I have seen some recipes that begin by making a starter by inoculating a small batch of material and letting it grow for a couple days then use that to inoculate the majority of the material.

Can I just fill my molds and keep back a bit of material and use it to inoculate another match of material?

Can I just repeat this as long as I keep things sterile?

Do the mycelium need to complete their life cycle? Will they keep growing if they never have the conditions to form fruiting bodies?

What are those conditions by the way?

Thanks in advance.

I did more reading and found this site. It answers most of my questions.