Proxmox 3 and DRBD?

Hi everyone,

Earlier I had a discussion with a friend and suggested to use this setup for Proxmox DRBD.

Server 1 (active) -> Server 2 (passive) -> Server 3 (passive)

Each server will have 2 VMs.
- App Server VM
- DB VM

Therefore,

Server 1's proxmox running - VM1 Start, VM2 Start
Server 2's proxmox running - VM1 Stop, VM2 Stop
Server 3's proxmox running - VM1 Stop, VM2 Stop

My questions:-
i. Why do I need 3 servers? Why can't I use Server 1 -> Server 2?
ii. If my Server 1 breaks down, will it automatically make Server 2 as primary? I assume it will auto-start my Server 2 VMs right?
iii. The tech specs for my servers as below.

Server 1 - 2 x processors, 32GB RAM and 1TB RAID 6 + 1 Hot Swap
Server 2 & 3 - 1 x processor, 32GB RAM and 1TB RAID 1

I assume DRBD will work for the above specs right? Or Do I have to get all 3 servers to be same specs?

Any help? Thanks.