First server & file sharing

Hi all! I'm new to the community and have been looking into making a NAS system using unraid. I have never done anything like this before and am trying to learn as I go. In my research I have come across a few things that are not super clear and/or I cannot find direct answers to; so I thought I would jump on here and see.  I would like to set up a NAS system to store media and important files as a sort of external backup (most if not all of this would likely be done manually). It will be configured as more of a storage rather than a streaming device. I have a large library of music and CAD files that I want stored in another place to reduce the risk of loosing them should something happen to my main computer. My questions with this are:

1. What sort of system should I use to run this (essentially how slow is too slow hardware wise). My current plan it so utilize an older refurbished computer to start, with the long term plan to build a nicer machine once I graduate college.

2. Is there a way to set it up so that my files can be accessed from outside my home network. My main goal with this is to create something so that my family can also store their important files on the machine too. They live a few hours away from me so I wanted to know if this is even possible. I don't plan to be able to access it from outside private secured networks - though if there is an easier way to do this safely I wouldn't be opposed to it so I can access files while on campus (if/when we ever go back in person). I am also open to incorporating a password login into the system for all users if that would help with any of this. I don't plane to do much management remotely, just wanting file access for myself and my family.

3. A bit of a side question - how hard it is to run a dedicated gaming server off a same machine running unraid? I understand the hardware requirements go up quite a bit but just more of a hypothetical one. At most, it would only be a single server for up to 6 people running games through the steam dedicated server setup. I have seen people post on here about similar stuff but they seem to be wanting to run multiple servers off one machine or very high performance games. Mine would mostly just be a single instance of Space engineers, minecraft, and other similar games.

Mainly I am planning on just using this as a way to learn about personal servers and a stepping stone to eventually get a nicer one. Questions 1 and 2 are the more important ones. Question 3 is more of just a curiosity since I would have a machine running as a server of sorts. I am planning on using unraid since it seems to be easier to learn/use and there is such a large community around it. 

Any other advice and/or precautions for a first timer are greatly appreciated!

Thanks in advance! - Forest