It’s not all doom and gloom - have a read of this thread:
Whilst the 720+ doesn’t have the horsepower Roon recommends, it has about half the muscle of the Xeon E3-1230 V2 in my RS3617xs. That runs a boatload of other stuff as well as Roon and doesn’t even begin to break into a sweat, even with DSP. Believe me, I’ve tried to break it - with Plex running 3 different 4K movies to 3 different TVs and Roon streaming to multiple endpoints plus 8 QHD IP cameras continuously recording, CPU and memory use were still very low.
Have a good read of the thread above - Christopher Rieke has ironed out most of the niggles apart from the library automatically refreshing when you upload new local content to the NAS (you still have to force a manual rescan)
As for installing via iPad, I can’t help there - I left all things iOS behind me nearly a decade ago. Strictly Windows/Android these days. My wife loves her Apple stuff, but I’ve worked with PCs since they needed floppy boot disks and I’ve used PCs running Windows in a business environment since the early 90s. Even familiar software such as Lightroom and Photoshop were alien to me in an Apple environment…
Roon recommends the Nucleus/Nucleus +
I get that, they have a product to sell. It’s not flawless, though. Lots of peeps have problems with them. Though, for the sake of balance, most people for whom they work flawlessly probably don’t post in the community so the reality is most likely considerably better than the perception.
An awful lot of the issues people have with Roon are purely down to network - crappy network topology or shonky wi-fi implementation. If it’s physically possible to connect via cable (Cat5e/Cat6 UTP, none of this exotic shielded Cat7/Cat8 sh!t), then cable it!
If Roon is on your NAS, then as far as the core is concerned, stored music is locally stored to the core.
What doesn’t seem to work quite as well, is a Roon core on another device with the music library on a NAS - the limiting factor here is network bandwidth and latency, and the ability of the storage array to saturate the available network bandwidth.