Hi jandrew,
cPanel is, as you may already know, managed via a database, I previously had dedicated servers setup by me from scratch so, as an example, a Debian 7 64bit, php, apache, mysql and postfix, from there I would just build clients over it. Is your intention to use WHM? Won't be easy to manage your server without it if you want to do it yourself but I believe you already know a few things about server management so you more likely to know what you want anyway.
Not sure if I am the best person for this job but can give you any support needed.
PCI compliance is a standard and we use it in United Kingdom as well, the question is how compliant should it be... anything that directly interacts with the credit card processor and receives data from it is not PCI compliance, anything that allows you to supply details and return just status code (auth/reject code, transaction id, etc) is compliant, to an extend which means it's ok to use if you don't keep any card details on your server other that the first 6 and last 4 digits of the card and not the CVV code.
In order to get sites to display fast you could extend your service with a CDN and cache content provider - I am not too confident with those to be honest, never did anything similar - otherwise you could offer third party services such as CloudFlare which is free for non SSL sites.
Anyway, I can help out in the future or even setting up your server but I am not an expert :)
Thanks for taking the time to read
Rui