First you have to decide which animals you'll be selling for certain. Then put them up for sale and get them out. Once those are out, you need to decide on what breeding programs you want to do, and what you will need extra to do those breeding programs.

Write the breeding programs out, remembering that if you buy hatching animals, you'll have to figure in the years of raising them. Now you'll know what space you will need total. Figure in a couple extra slots just in case.

Figure out when you'll actually be breeding, and then you'll know when you will need hatchling racks for the babies.

Once you do all that, you should have a list of how many animals you want to have when. That gives you the number of slots in potential racks, and you can order up your racks(or buy them at a show, save on shipping) and figure out where they will go(don't forget a quarentine area somewhere away from your animals!! Very important!).

All that should get you started.