Cloud Computing Architect Needed - Java PaaS Recommendation

We aim to build a web based tool that will help users browse through, and manage, large quantities of data. We aim to have about 500 active users who, each, might use the system for about half an hour a day. We want to run the system on a cloud computing platform, a PaaS. Our server side language of choice is Java. The web interface must be lightweight for maximum browser performance. We need a production environment where we can release new functionality incrementally, as well as have a separate beta environment and another separate testing environment. Performance is our number 1 metric. We must have a fast front end. We have a stateless server but would like to use in-memory caching to help improve performance. We want a cloud computing architect to help us decide on the following: 1) Which Java PaaS vendor e.g. heroku, cloudbees, etc. to use and how they potentially could compare from performance point of view. 2) What front end technologies to use (apart from standard javascript, css3, jquery and html5). 3) Any other frameworks that we need to consider e.g. Play, Scala, etc. 4) How in-memory caching can work (given that some PaaS like Heroku don't automatically support this) 5) If http session replication is automatically supported by the platform, and if not, how to support it. 6) If we can have an environment where we can do continuous integration. You can either write up this info or we can go through it on the phone. Looking forward to hearing from you.