Your approach was largely correct. You've not stated which router you have, but I'm guessing one of the ER-X models or an ER-PoE.
As long as you set an IP on a different subnet for each LAN port, and define separate DHCP scopes for each subnet, the router will route packets between all the LAN subnets and the WAN.
Controlling what can then talk to what on other subnets is simply a matter of building the correct firewalls.
I'd suggest you set up the IPs/subnets for each LAN port along with accompanying DHCP scopes if you're comfortable doing that, and then posting your config, along with a description of what you'd like each subnet to be able/not able to connect to and we can help with the required rules/syntax.
To post your config, copy and paste the output of the following, redacting anything sensitive:
show configuration | no-more