I have it running on my server, and honestly… I almost love it more than kagi. Still evaluating both, to make a decision by the end of the year.

are they even actively developing it? repo seems abandoned

I would suggest not to rely on that. Give the DHCP a range, use manual IPs outside of that range

Haven’t done it myself, but his might help you for further research

iptables

https://unix.stackexchange.com/questions/264589/traffic-of-specific-program-through-vpn

network interfaces

https://unix.stackexchange.com/questions/234583/routing-on-per-application-basis

I’d recommend the following, which is what I did

• Get one of these N100 or N305 firewall mini PCs with two NICs for your opnsense box. they’re like 15x15 cm in size
• A managed switch (at least 8-port)
• A cheapo small PC case, that can house enough drives, or can add some 3dprinted drive tray or whatever for your NAS.

I’d highly suggest, not to put everything in one box. Been there, nothing but struggles.