haha, I went from just wanting to buy a cdp to building a computer ! Hummmm. Getting into the weeds here now. I know punters are module and clic together. And diy is a real good way to go in near anything. Roon is setup to be as close to plug and play as they can get. I just want to get my remaining library into the mix and have easy access. My mini is a weak link and my storage device has a fan I don't care for. Be nice to one box that with modern gear. A better dac would round that out nicely I'm thinking but a real server/stereo and great dac will always beat a streamer I would bet. So many paths. 
I went from using a $1400 laptop with an external HD and a 1TB SSD to my custom computer and the difference in sound was remarkable. Even using shielded SATA cables make an improvement in detail. There are some great motherboards out their that use premium capacitors. Low noise and low ripple power supplies like the Corsair RM-550x make a huge difference. It also has a quiet on demand fan that really never spins up. There are even better ones. I also use a Fractal Define R5 quiet case that is modular and hides all the wires. It has pull out dust screens to vaccuum and it truly is quiet. It has usb ports on the top front besides the backside. The power supply sits on the bottom of the case vs the top (the bottom is better IMHO). I bought Noctua quiet fans that are about 11db to cool things. No video card is needed for audio. And no monitor is needed except for initial setup.
If you build your own server, then you can run HQ player inbedded in Roon for better sound quality. With a good I-7 CPU and 16gb to 32gb of fast ram you will have no problems upsampling and using all the filters in HQP if you so please.
I just added a JCat usb card, version 1.1 that I bought used and it took my system to another level of improvement. The sound is just stunning. It further improved when I added a cheap Teradak Linear Power supply and then another improvement with a Wire World Starlight 7 Platinum usb cable that I bought used.
If you decide to build one, wait until Thanksgiving as parts go on sale. I saved a few hundred dollars buying parts around that time.
Of course, you can buy a custom computer from Falcon NW computers and customize as needed. They use Seasonic power supplies which are great. They will set you back about $4K. It is much cheaper to build one yourself.
https://www.falcon-nw.com/desktops/overviewGood luck on whatever you decide.
A NUC is a good way to go but with building your own, you can use better parts. I have 2 friends that use NUC's and love them. But it is nice to have all that internal storage with a custom computer.