"Need" Roon, Bluesound Node, or or other streamer?

You are really asking about three separate things:
User Experience Software (Roon vs. BluOS)
Playback Hardware (which requires 3 parts: streamer/renderer, library storage
Control Hardware(tablet and/or phone)

I'd suggest watching some youtube videos of users demonstrating use of Roon(e.g. Hans Beekhayzen) and BlueOS and decide what experience you'll be happy with. For me, Roon was a game changer and I can't imagine going back to any other app. It makes choosing what to play more fun and increases engagement. This also applies with family and visitors. 

If you head this direction, building a NUC or buying Small Green Computer products both will work great. Internal storage vs. NAS(e.g. Synology or QNAP) for you library really depends on size of your present & future library.  

Any of the above and the Blue Node will all sound better than most Mac/PC setups unless you go to great length and cost to overcome those platforms disadvantages(e.g. NOISE, frequent OS updates screwing things up, many others)

Yes, your DAC is probably way better than that in the Blue Node and I agree that MQA is a sham. I would suggest not making MQA part of your rationale for choosing your path forward. Use your external DAC and a tablet/phone/mac as remote for any of the above. Cheers,
Spencer

Not easily. PCs, especially in the same room and connected to the audio system generate noise. There are many ways to try to overcome it, like external linear power supplies, dual-headed cables that separate signal from power, etc. All the background processes supporting other stuff your computer does are something to overcome. Low power dedicated devices with more of the parts cost dedicated to what affects audio has generally proven a more cost-effective approach. 
Let alone the UX impact of OS updates messing with music software on PC or Mac. 
Many of us had PC or Mac based rigs and moved away from them as better alternatives became available. the majority of posts on computerlifestyle (formerly computeraudiophile) address many subtopics that apply. Cheers,
Spencer 

Aurelic Aries is very good sonically assuming you're using it with their or another high quality linear power supply. Current models are Roon-ready, but if you're getting an older one, it's worth confirming that it's Roon-ready or you'll be stuck with their proprietary software, which is pretty good, but not as engaging as Roon. 

An advantage IMHO of the bridge approach is that you can invest in a NAS based on the size of your library and keep the NAS in a different room allowing you to use standard disk types (e.g. Western Digital Red) instead of having to pay for SS drives(quieter but much more costly). 

Another worthy line of "bridge" devices aka renderers is Sonore, which I am biased towards, and feel offer the most sound quality and flexibility for the cost, along with superb support...especially if purchased from Small Green Computer. Cheers,
Spencer