Server admin for a two part project

We are currently developing a SAAS service of a website that will hold many different subdomains (similar to [login to view URL] that has many subdomains). The application/website currently runs in a dedicated and a VPS server. The dedicated server runs the website (and all subdomains) and the VPS runs certain scripts that update the databases. One of them runs on Linux CentOSand the other one runs on Ubuntu. The dedicated server has Plesk panel. I am looking for a server admin who is very knowledgeable and that can help me in the following two part project. First part I would like you to recommend me the best server architecture for this site for the future, understanding that it needs to be able to scale up very easily and in an optimal way… So at the beginning (now), the application will have very few customers but as time goes by, it will have more and more traffic, with some subdomains having much more traffic than others. A solution such as EC2 (or similar) seemsto be the most suitable solution, but I would need to know how it would need to be structured optimally so it can grow, well. For example, where would the (common) code be located, the subdomains, databases, etc, so that I can grow well to an infinite number of subdomains having each one of them different traffic. I would explain you how the website works and you can see it live on the dedicated server. For this part I just need an explanation, proposalon what would be the optimal site architecture so it can scale optimally, according to our needs. Second part: The dedicated server is not working efficiently now and I would like to see if you could give proposals on improvements on this. You should be able to debug specific Apache &PhP errors logs and 500 Internal Server errors and suggest improvements. Should be knowledgeable about mod_FCGI module. I like to do many different projects with the same service provider and I am looking for a server admin who can do all the projects I have related to server admin. If you do a good job, I will request more things from you in the future. You should be available for Skype call, to be able to speak with me and/or the programmer for better understanding and ease of communication for this project. My budget is limited, so please sharpen your quote.