What I learned in my partially failed, long running experiment setting up my home network / entertainment system for the future:
1- Do not run any Streaming Video from Internet or from local network on WiFi.
2- If you have an A/V Receiver (AVR) in your setup, make sure every input is wired to it.
3- If you have an AVR in your system, make sure AVR is "The Boss"!
If you have an AVR you probably have surround speakers as well, the only route to your surround speakers is through your AVR. So, do not let any component skip AVR and connect directly to your TV.
That means you should plan on playing your (AVR Supported) audio from your DLNA Server through your AVR, NOT Through the TVs SmartHub or equivalent. For Video content you should get a NAS Box with built in player or a separate player Connected To Your AVR. You can play local video through SmartHub but you may encounter sound issues if the content has built in surround sound and you DO Want to hear the built in sound when you play the video file.
3- Keep your equipment in your TV Room unless you really really have to have them at a remote location.
4- If you are going to do any kind of {SIGNAL}_Over_CATx, You ARE going to encounter problems!
Especially with HDMI Over CAT5/6/7 (CATx), you will encounter many issues from hiding the power adaptors, HDMI extenders behind the TV to getting the Audio Return Channel, ARC to work.
5- Always plan with Expandability and Control in mind. Plan HOW You are going to control various components simultaneously. Plan and purchase considering future needs and expansion options.
On the NAS Issue, I would consider my lifestyle and try to estimate how much storage space it would demand. In my case, I have some 20+ years of camcorder and camera data in my basement storage that are waiting to be digitalized and stored in a NAS. I generate 32+GB of new data every week or so.... You can see where this is going.... If you want to live in your home for 20 years, you should be buying a NAS device that can handle 60+ Terrabytes of data.... Your lifestyle would probably demand much less than that and that should tell you not to overpay for something you will never fully utilize. General advice is, if you are serious about NAS, get something with at least 4 Bays and Always buy the highest possible capacity drives for your open bays! Unless the budget is a major constraint, Get a NAS Box with built in Uninterruptable Power Supply (or an UPC for your NAS in a seperate box). Also the NAS box should have the most robust RAID options available. At this end, I do not see any major competition to Synology for Advanced Home User.