NAS + Host Check

[Efficient_Good_5784]

Looking at the pcpartpicker list you gave, I would say it would work fine for needs. Just make sure to enable HWA since that's more power efficient and can transcode much faster than the CPU alone can.
You can look at the Node 304's "bigger brother", the Node 804. With the 804, you have the space to put in a full-size CPU cooler too (don't know if you have one on hand).
Also, if you need the NVMe drive to be 1TB, you can upgrade the 980 Pro to the 990 Pro for like $4 more. Though I would say you could probably look around for a cheaper NVMe if you're only going to host the OS on it and never use it for anything else.
https://pcpartpicker.com/list/KgnnKX

By the way, I would be worried about the NAS being on a boat.

1. Humidity and salt in the air would be a concern. It would be best to not have as much air blowing through the system to prevent rapid corrosion of the metals in the PC.
   
2. Since boats are on water, the rapid and/or constant movement of the boat rocking would be concerning with regards to HDDs since they now have to handle all the excess vibration and movement.
   
3. I would assume electricity is at a premium when on a boat. SSDs would be perfect here since they use way less watts than HDDs do. SSDs would also help with my point #2.
   

You also say you want to host 16TBs worth of data. I'm assuming you're going to run some type of NAS OS since you are choosing NAS-grade HDDs.

1. With just 2 8TB hard drives, you'll have to strip them together to reach 16TB (14.5TiB) worth of space. If one drive fails, you will lose all the data (if both are on the same pool of data that is).
   
2. If you're not going to be using NAS software and you wont be adding both drives together in some sort of pool, I would look for non NAS drives. NAS and server-grade HDDs are set up to rely on other similar drives within some sort of raid setup when dealing with unreadable sectors on their disks.