Does anyone know where I can find guidelines for multiple server roles? I am
not having much luck finding info on this. Which roles are ok to mix and
which are not reccommneded? Can a domain controller also be an application
server? Some reccomend not. Can a domain controller run SQL and be an
application server? Can that same server run DHCP and DNS without problems? I
understand that the hardware is going to be a factor. I am more interested in
conflicts or problems with the software. There should be a whitepaper or
something out there regarding the do's and don'ts of mixing server roles, Microsoft applications and
services on a single server.

I dont see any issues running all those services/applications and server roles as you described. There shouldn't be any issues what's so ever.

We have found problems with running applications on our domain controllers. If the domain controller goes down, we have the emulator as the backup and we can rebuild the DC with no down time. If you have all your applications on there also, you will have to restore all the programs as well as your active directory. There is an article on the MS site about managing the FSMO roles. I have it printed and refer to it often.
It's old so I don't know if the URL is current. It is printed on the bottom of the page as: sorry the rest is cut off. Hope this helps.