IT manager – DHCP, DNS, printing question

I am new to my organization with 7 different sites and I wanted some feedback.

We have 2 DNS servers, 1 server also acts as the DHCP server, print server and file server. These boxes are towers and around 5 years old. I believe they need replacement but am not sure.

What is the best practice for setting the standard DHCP, DNS, print server and file sharing environement in any network?

Do they each neeed their own server. What is the best topology for a robust environment?

Thanks.