I'm getting UFB connected over the next couple of days (first lot of techs are here at the moment).  Currently, most of my devices are connecting via wifi but I've been thinking about a wired network so I can take full advantage of UFB speeds.  I had contemplated getting under floor myself to run some ethernet, but the techs have offered to drill a couple of extra holes and feed tape through so I can pull through the ethernet cables myself without having to get under the house.  This isn't the perfect solution (basically just a few ethernet cables directly connected from the router to the devices currently using wifi), but it will be better than wifi.

But my issue is the number of ethernet ports on the router.  It's a Fritzbox 7390, so it has 4 ports, but one will get taken up with the ONT connection, leaving me with three.  In the same room I have an Xbox 360, a NAS, and an ethernet-capable TV and Blu Ray player, plus a laptop or Pi for hometheatre duties.  I haven't had everything plugged in (the TV and Blu Ray player aren't important, but the laptop or Pi, plus the Xbox and the NAS are important.  And if I run three direct ethernet connections to the other rooms (which each have one device), then I have a deficit of three ethernet ports.

Short of getting a properly-wired patch panel (which would be better, but more complex and expensive), what's the best way to expand the number of ethernet ports I have?  Do I need to get a switch?  I've heard that sometimes an old modem/router can be repurposed as a switch, by turning off the modem and DHCP functions.  I've got an old Linksys round here with four ports, so would that work?