The main issue here is that you essentially just want it to be a switch and not a router, which is going to be problematic if you intend to pass traffic amongst them in different ways.
The way you're describing this working would be routing traffic on the uplink port to your router from the other interfaces. You'll need this because a stock Debian install runs network interfaces as clients and not routed interfaces that pass traffic. You're basically building another router and making certain other ports switch interfaces.
This is a bit more complex than just getting a $10 cheap unmanaged switch and hanging that off your router for extra ports, but if you're determined to go this route, you basically just need to look up routing traffic in Debian and you'll find some guides.