Hello. I will need servers to run an application and website. I don't know if anyone can recommend a good host?

One problem I have is that it is difficult to give precise demand estimations and hence estimate resource requirements. It seems flexible cloud-based hosting would solve this problem by allowing for easy scaling of resources. I see some hosts offer automatic scaling systems which would be the easiest method and protect against downtime or lag from overload.

The servers would need to be very secure, so any host would need to abide by the best security standards. The application wont be managing debit/credit card information but hosting that keeps to PCI DSS standards would be a bonus. And yes, I do know the application needs to be secure.

The application will need to be vey reliable. Any downtime at all can be very damaging. I understand that it's impossible to expect 100% uptime with any host but I've come across Round Robin DNS, DNS Failover and BGP failover that can switch websites onto new IP addresses in case one IP is unavailable. DDoS prevention is obviously a factor too. Does anyone have any advice for providing the best uptime possible?

I will get some expert guidance on this further on so I can ensure all my requirements are met. For now I need a reasonable idea what to expect for a business plan.

Thanks.