Configuration recommendation?

Hi all,

I would like to build a dual Opteron 242 system that will
be running Linux in 64bit mode. So I have several q's:

Must the cpu's be "matched"?

Will I have a problem finding/getting a second cpu if I
start out with just one and try to add one latter (for
price reasons)?

Which manufacturers (mb) have a better reputation for
reliability and support, speed is secondary?

If you have gone through this, any helpfull hints would be
greatly appreciated.

thanks,
charles.....