This is likely an easy one, but I have EXCLUSIVELY used Mikrotik routers as routers and never as a switch. Each LAN or VLAN on the routers connects directly to a CSS326 switch. I have run into a situation where I have run out of ports on one of my CSS326 switches and have an immediate need for a couple more ports. If I was not in a hurry, I would just order another switch. I do have a RB750r2 that had been replaced with a RB750Gr3 a while ago and is therefore spare, and should be able to be configured to operate as a switch. Below is a drawing of the intended layout.
Under normal circumstances, ports 2 - 5 will have VLAN 2 connect to each other. That will be at least 99% of the traffic. VLAN 1 will connect to all five ports (although will not likely ever be used). Untagged traffic from ports 2 through 5 is also not expected to ever be used, but will each be assigned to a VLAN (VLAN 302 - 305 for ports 2 - 5 respectively) and sent to the CSS326 via the trunk port 1. VLAN 101 on Port 1 will be for management.
I can handle the firewalling for keeping the VLANs apart, etc. I just need to know how to make the router play switch. I could do this in SwitchOS in a heartbeat - if I was using a switch...
In case you are wondering, AREDN is an amateur radio data network.