Networking Question

I am new to networking and am configuring a NAS so that I can store all my photos/videos and whatever else I need. I didn't have the budget to get one that could do much streaming and forget about 4k...it was the DS220J from Synology in case that matters. I plan on temporarily using my main PC as a media server (which is more capable in specs) whenever someone in the house wants to watch a movie, but my question is how I would set up my PC to operate as the media server (playing or transcoding the streams), while keeping the actual files or data on my NAS.

I typically keep my PC on most of the time already so that isn't really an issue for me although I wouldn't plan on leaving it on 100% of the time, especially since it would be getting more use if I used it as a media server - it's got a 1080 TI , 7800X, 64 GB RAM, and supports a 1 gig link aggregation, but my worries comes from the fact its an 34" all in one in a tight enclosure with a 450 watt power supply already pushing some pretty extreme measures (although no current issues in over 2 years).

I have an ubiquiti 8 port switch that is fully managed although I have no clue how to manage it yet other than connecting the ethernets together. Is there anything I should be aware of and what is the process for accomplishing what I need, other than setting it up and connecting the ethernets.

I have plans to also access videos remotely outside of my local area network - would that be possible using my media server connected to my NAS? If so, how would I do that?

Sorry for all of the questions, just new to this and don't want to screw anything up since I am already balls deep in cash that I have spent