One word of advice is to maximize the efficiency of the set up before you begin to accept animals. I suspect that a single room could house quite a few animals if the design is good. You should also research some protocols and products that will be useful in preventing or minimizing spread of pathogens (and potential illness) as the greater number of animals housed per unit volume will likely increase the likelood of problems arising. If you plan on accepting snakes and monitors, then a small rodent colony will also be a good idea.