BeerNCheese

If it's just files you will be doing, than you should take a look at seafile. It's easy to setup, it works better than OwnCloud (or NextCloud) and after setup, you will have an admin account from which you can add users/groups, storage quota's per user, and many more functions.
You will also have dropbox-like clients for Linux, Windows, Mac, Android and iOS
 
Take a look at the manual, it will give you an idea about all the features

If the Ethernet Cable is CAT5, I doubt you're running enough length in your house to cause problems. However, if it is ran through/by anything that gives up an electromagnet field, it could cause connections issues. 

A: Upgrade your wireless equipment by either purchasing a new NIC, Wifi Range Extenders (This is supposedly shotty, never personally used one), or hardwire your laptop the the network. 


Also, what software/configuration are you using to cast your movies? Some software may be causing the issue. 

The front of that case looks starved for air.