Need Implementation and recommendation for SMG

hi everyone,

I have a client which is ISP provider and email service provider, they want to purchase SMG as anti-spam for 240,000 email user. My question are

a. what is the best approach  SMG appliance server or Virtual edition

b. how many SMG scanner and control center?

c.if virtual what are the SPECS of SMG.

d. how do i configure the mx record? do i point mx 10 to scanner 1, mx 20 to scanner 3. or mx 10 to control center?

if you have diagram to share with multiple scanner  deplyment , i wouold really appreciate..

thanks everyone in advance