What is the correct way to set up multiple subnets?

Something tells me that adding a second IP address to the primary interface in my EdgeRouter Lite is not the right way to go.

 

I have a Windows AD Domain set up with DHCP and DNS, and I would like to have different subnets for (for example) all of my smart switches/plugs, the "work" computers, "personal" devices, etc.

 

How do I accomplish that in terms of network infrastructure? I know how to add the subnets in Windows Server, but do I need to have multiple NICs in the server, one for each subnet? Should I add multiple IPs to the same NIC?

 

When I've tried this in the past (probably did it wrong) the biggest issue I had was domain name resolution across the subnets. Devices in one subnet could not access devices in the other subnet by FQDN. I imagine this is because the DNS was not set up to correctly operate on one of the subnets? How would I go about doing this properly? I also have this problem with accessing devices across my IPsec site-to-site link, and I assume it's the same (or similar) issue?

 

I'm sure there are other things I'm not considering, so feel free to tell me why this is an awful idea and I have no idea what I'm doing (accurate)