How many Domain controllers would you recommend for a system with 1000 clients and 50 other items that all need to be able to access the domain? Why did you choose the numbers you did? What factors...

How many Domain controllers would you recommend for a system with 1000 clients and 50 other items that all need to be able to access the domain?  Why did you choose the numbers you did?  What factors should be considered when deciding the number of servers you need?

How about if the system was just 50 clients and 10 other items?  Explain.