Question : Help building a server to host virutal machines

I have been researching virtual machines and have come up with more questions than answers.    I cant find any guidelines for specifications so I thought I would try here.

1.   First microsoft or vmware?
2.    How many virtual machines per physical machine is practical?
3.    In the case of microsoft Virtual machines should the host machine be left alone and not provide any function other than hosting the vitual machines?  For example could your host be your domain controller or print server?
4.    memory resources are fairly easy to calculation but I am having trouble with processors, hard drives and network cards.    How many virutal machines per processor?  How many virtual machines per network card?   What is the best raid configuration to get the best performance and fault tolerance.   Should the host operating system be on a seperate raid?
5.   Is it better to build medium power system to host 4-8 virutal machines or build monster systems to host 20 plus?

I know these are all going to be a matter of opinion but I am hoping I can get some guidlines out of this.   I will split points amongst whomever provides what i am looking for.

thank you

Answer : Help building a server to host virutal machines

1. I use Hyper-V. I like it
2. Depends on RAM... I have 3 VM's with 8/8/4GB ram, host machine left with 6GB (24 total)
3. You can add roles to the host machine, depends on the resources allocated.
4. 1 Physical NIC per VM + 1 for the host, RAID 10, SCSI or SAS drives are better for performance, processing shared, Host OS on RAID 1 array separate from Data.
5. Really depends on the requirements. Always plan ahead.