SP/Web Hosting Design

Hello /r/networking,
I've recently started looking towards network design and I feel a bit lost. Specifically about SP/Web Hosting networks, how does the design of these networks for these differ from, say, Campus design? One of the topics I wonder about is how separations is handled. Say if a Web Hosting company has 5k+ customer servers - how can one separate each and everyone from each other? I assume assigning a VLAN to each customer wouldn't do.
How about security - Redundant firewalls for the entire customer network as well as the internal network? Or keep them separate? Multiple redundant firewalls for different purpose?

 

I have a lot of questions, but I don't really know where to look. So I'm asking here - Are there any good resources out there on this topic? I'd appreciate any pointers, thanks.