Using MongoDB + Redis + Apache on the same server in production?

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http://serverfault.com – I intend to launch my web app using a 8 GB VPS. It uses MongoDB + Redis for storage/caching and Apache + PHP-FPM for serving requests. Could there be any issues with running Mongo + Redis + Apache on the same server? Would it make more sense to setup 2 x 4 GB VPS servers and keep Mongo on one and Redis + Apache on another? Should I just start with one server and worry about scaling horizontally later by delegating the existing server to Mongo in the future (due to its large RAM) and moving the web servers on to multiple smaller VPS'? (HowTos)