Two servers will be the best solution. This way you can easily expand and add more into the cluster. One will be dedicated to MySQL and the first "node" will be assigned to web traffic and running the board itself only. As your needs grow, you can easily do round robin load balancing and add in another httpd server....
I would highly recommend making the MySQL server raided across a 7 disk array because with boards, especially busy ones, the disk speed becomes a big bottleneck.
We can config all of that for you with no problems and pretty fairly priced as well. Give us a shout.
http://www.splitinfinity.com