Ubuntu Server Advice

I'm trying to plan a home server, would you please offer some advice on whether this is practical?

- CPU, intel i7-7700
- RAM, 16 GB DDR4
- HDDs, 1 x 512GB NVMe for OS. 4 x 8TB WD RED in RAID 5.
- I can add a GTX970 I've got laying around, but I'd prefer to avoid a GPU if I can.

I am planning to use it primarily for Samba/data storage and Plex, although I'd like to have enough grunt for some small projects and future proofing. Not planning on VMs, although I might play with docker or something.

This will be a headless server. I was thining about TrueNAS but advice I found on their forums was unless you're going to spend hundreds on ECC capable memory, CPUs and Mobo there is no point.

The shares will be accessed from a mix of Linux, MacOS and Windows computers.