The answer you would probably expect is "well, it depends!" Not exactly helpful, but accurate.
It does depend on the expected load the merged servers will be under.
For example, I am in a 50 user office, and we run DHCP, WINS, 4 print queues AND the home directories ALL on the PDC!
(I did not set this up, so don't blame me! I realize the single point of failure this is, but this is how they did it here!)
But to be honest, a 500 MHZ PII with 512 MG RAM is handling the load. During the day, the processor utilization is low. True, at 9AM, it does spike some, but even then it is only in the 50% range.
So for this office, running all of these processes is ok.
Now, if we had hundreds of users, then there would be a problem.
But it does meet our needs, and works just fine.
So in regards to your question, it really does depend. How many printers do you want to set up on the machine? How many user home folders? I would think that a single server could handle a couple dozen printers and hundreds of home folders, but others here will have better real-world experience in this.
Do I suggest putting everything on one box like I have? NO!
Unless you have a small office, then you can get away with it.
hope this helps