1. ECC, non-ECC: depends which board you choose.
2. CPU: depends what you want to do with the rig. I have E5504s (currently on loan with Chilly) and I use E5520s in my Main.
3. Boards to fit the Raven: SSI-CEB, ATX form factors.
Newegg.ca - Computer Hardware,Motherboards,Server Motherboards,Dual LGA 1366,ATX= and
Newegg.ca - Computer Hardware,Motherboards,Server Motherboards,Dual LGA 1366,SSI CEB=
Most have a single PCI-e slot, some have dual.
Overclocking is not an option on those boards, SetFsb may work if the clock generator is recognized.