Looking to upgrade the NAS I use to stream files around the house

Hi folks.

Hope this is the correct forum as I just removed it from networking forum and placed here.

Looking for some advice regarding an upcoming NAS purchase.

Currently have a readynas NV2+ which is about 4 years old. It has 8 TB of storage over raid5 and has run out of space and is getting old. A good excuse to spend some $$$ on a shiny new tech toy

Am looking to supplement it with a newer / larger capacity model but am typically an overbuyer and will spend monies on features I probably don't need or indeed understand so would appreciate some feedback.

Primary Use

Backup of all photos, media, digital files from main desktop PC - Requires about 10TB currently.

Backup of Laptops and associated files from around the house. Email accounts. Pics. Documents, PC images for reinstall etc

Use to stream to several media players around the home - an NUC and a couple of raspberry Pi boxes. These are currently running XMBC or Kodi. I have a wealth of DVD's and Blurays that I access digitally. Might stream to PS4 and or XBOX1 if possible.

Plan to install a number of IP cameras around the home and use NAS ( require some licence purchases ) to monitor and record.

Easy interface for control and managing user accounts / access to media as it ranges from cartoons to 18+ movies.

To date have been looking at Synology. Looked at the new DS 916+ and it seemed to get good reviews and can transcode as well although I don't reckon I'll have much 4k content. A friend has the Synology DS1515+ 5 Bay and swears by it. He has recommended the DS1815+ as it provides 8 Bays for not a lot more in the longer term. His experience is more space is always useful and his approach is to now maximise that in the first instance even if you don't need it today. I would plan to populate with 4 x 4TB Red drives in first instance.

Another friend uses QNAP and is pointing me towards the TVS-871 I3 8 Bay model as it has a huge amount of grunt for transcoding PLEX as well as running multiple streams around his house. From what I've read the older processors on the Synology kit struggle with PLEX etc.

So this is where I have gone from spending approx $1200 on a base model to $2800 on a base model with drives on top. I'm thinking that's overkill and while I like shiny toys, I'm not convinced it's monies best spent.

I'm not even sure of the benefits of PLEX for example or if I even need it.

While I appreciate tech is out of date as soon as the buy now button is pressed, the Synology kit is now 12 to 24 months old as a platform and I keep reading about their latest and greatest being around the corner in the next few months.

I'd probably use my older NAS to backup the critical pics, images, documents and movies so essentially would have 3 copies of them ( albeit on one site and network) - Desktop, New NAS, Old NAS.

Any tips, pointers, straight out advice or further questions to make me think about this from a different angle appreciated.

Cheers

Ged