Know that every abstraction will break at some point in growth. You haven't yet validated your hypothesis. Start validating your hypothesis with whatever you know. Once it is validated, which means there is enough traction, you will be able to attract people who can scale.
Choose Go. Marco (of Tumbler & Instapaper famous) choose Go and cut his servers by half. If you think he doesn't know PHP, you only have to consider that he scaled Instapaper only on PHP and sold it well. BeeGo is a good web-framework, if you need one.
Jan Vladimir has given you enough information. If you are still looking for something specific, you need to mention it. In absence of it, anything I (or we) says will come with some judgement that we make and that won't help you.