I need a NAS OS that's friendly with Spectrum provided router
As stated, I'm trying to set up a NAS that plays nice with Spectrum-provided hardware. I'm not the home owner, and the home owner will not budge on using a third-party wifi router that would just act as an access point. I'm trying to set up a small NAS that my friends can access via VPN connection, and I would remote desktop into for administrative needs. I considered Windows Server, but I wouldn't be able to have it connected to the internet while I set routing and remote access settings, so something that can pick up a DHCP addrese on its own.
I was under the impression that a VPN connection would be encrypted, and since I'd be still making accounts that would have to be signed into in order to access the data, someone attempting to steal the data would have to have the credentials to do so. RDP access (meaning full system control) would not be set up outside the local network, and remote access would be done through Windows Server VPN.
xpenology.org - Synology DSM on Your Own Hardware. This way, you can set up your own DHCP and manage the system just as if it were a Synology. I have not done this, but I like the Synology DSM OS. However, I do have experience with Windows Server, and it's not as secure as you might think, unless you know all the steps to take. Otherwise, you might encounter security problems. You might also wish to get your own router and have Spectrum provide just a bridged network connection.
If you would like to get fancy, Asus has its own VPN and DHCP services, and most of their higher-end routers include built-in NAS services. I also recommend Pi-hole, so you can manage all DNS requests and create your own local domains, like movies.local and music.local. This allows you to set up the VPN, and all your family and friends can just type in domains for device addresses.
If it were up to me, I would not use their equipment and would instead use and configure my own router.
As stated above, I don't really have that option. I don't own the home, and the homeowner isn't willing to bend on switching off the ISP-Provided router, and modern spectrum routers can't be configured to bridged/access point mode.
Spectrum will provide a modem only and let you use your own router and AP, but if they won't budge on anything regarding it that's probably not an option.
What exactly are you trying to accomplish though? What will your friends being doing with your NAS? Spectrum doesn't have great upload speeds so at best they'd get slow downloads and at worst it would make your internet unusable with them maxing out the upload.
Using my powers of total ignorance bolstered by who-gives-a-crap self confidence, I just plugged a second router into the ISP router. That's the one I put all of my custom settings on. Waiting on other comments to tell me why that's a bad idea, but it has worked so far