I've thought about doing 3 Linode servers installed with centOS/cPanel. So we'd have 2 web nodes and one MySQL database server. The 2 web nodes would need a fast replication system so that I could change a file on one and it would be on the second web node within a very short period. So, on fast replication,
You may want to look into a cluster backend and multiple frontend servers behind a load balancer.
I don't think NFS will be fast enough -- right? I mean, NFS might have like a delay of several hours, right?
NFS is a file system so should be very fast. The problem is when NFS hangs, but that should not be a problem in your case.
Okay, the above is all well and good, but the trouble I'll have are some of the heavy duty Linux tasks such as fending off DDOS, anything more than simple firewall rules (I'm pretty good with iptables, but not good enough to fend off DDOS), advanced DNS, advanced mail config, etc.
P.S. My background is that I've had a taste of some of this while working at ADP. There, we used 1U servers (and eventually, blade servers) and built all this using Suse Linux. (I'm not a fan of Suse. I prefer centOS + cPanel. I would probably prefer Ubuntu Server, but Webmin is so dang hard to use with it for doing mail configs, DNS tasks, setting up FTP, etc.)