I'm currently using QNAP TS-453d (4 bay NAS with 2x 2.5GbE) fitted with 3x 4TB Seagate Ironwolf HDD config in Raid 5.
Plex works fine and did streamed 4K video over internet. Continuous upload bandwidth consumption is around 5~8Mbps (dependent on how the movie was encoded) with peak @ 12Mbps (during start of video for buffering). NAS transcoding capability is subpar even @ 1080p. So to avoid buffering @ client and hammering of NAS CPU, best is to avoid any transcoding at all.
Some tips to avoid transcoding @ NAS
For videos stored @ NAS, try to use SRT subtitles (a separate very small size text file) and avoid embedded subtitles with image type and/or .IDX and .SUB file type of subtitles.
For client side, change video quality to ORIGINAL or Maximum (default settings @ 4Mbps 720p) especially for remote streaming to avoid transcoding by Plex @ NAS to client.
For LG and Samsung smart TV, on their app store, they do have Plex app for free and that certainly help to reduce clutter. For android TV boxes or TV (e.g. Sony) loaded with Android TV OS, Plex app is free with no limitation while the rest (e.g. mobile, tablet & etc), there's a 1min limitation or you pay USD5 to remove the limitation.
Backing up photos from PC, mobile or tablet to NAS
There's a QFile app (from QNAP) available for both Android and iOS client. This app will help to upload the pictures in your device to NAS. Currently, I set the app in "mirror" mode whereby it will upload your selected folders to target folder in your NAS. In iOS, it's restrictive, it will upload all images (including WhatsApp pics on top of those that pics taken by camera).
There's another app from QNAP, QSync which I did not like it. After sync, you will not be able to see those files from desktop PC as it's hidden and doesn't support Windows SAMBA file access. And for Hybrid Backup Sync (see next topic), by default, it will not sync hidden files as well. You need to force it during the profile setup which is more job
For desktop PC, I'm using FreeFileSync software to sync between PC and NAS.
Hybrid Backup Sync
There's an app within NAS app store (from QNAP) that allow you to set automated sync between NAS and cloud (quite a huge selection and including Amazon S3). So for selected folders, I set a weekly sync to OneDrive for added redundancy.
Others
There are many apps @ QNAP app store which also include torrent client as well (I did not use it). Yes, it does support VPN with their QVPN app.
QNAP may not be the cheapest (compared with other brands and DIY) but certainly, their ecoSystem are not too shabby and save you the trouble from running around to get different app to work together.
Take note, not an expert user (novice) so the above content maybe outdated or incorrect. Do check it out.