Q1: It's your personal preference. I would go with the language you are most comfortable with, or the one you're least comfortable with if you really want a "challenging project" like you mentioned. In either scenario it really does come down to personal preference so it's hard for me to tell you which one you should go with.

Q2: If you want with the PHP/Laravel approach you can have the main node run the full Laravel framework. Each other the child nodes can run Lumen with there own API which can be used to between the master and child node. To fix your current problem though I recommend going with something like Node.js for the master node. It's evented/non-blocking architecture will allow you to quickly handle lots of requests. However if you only have 5 nodes I don't see a problem with sticking to Apache or Nginx.

Hope my answers help in any way, Luke