The ADSL modems which I have seen ... even the ones with only a single Ethernet port - will handle quite a number of simultaneous logical connections. The number of at least 32 is in my head.
The practical effect of this is that you do NOT need a router, an Ethernet (packet store and forward) "switch" is plenty adequate in most situations.
You can both be using your wired Ethernet computers simultaneously when connected to the ADSL modem through a "switch".
In an office where I volunteer, the two computers share a single-port ADSL modem using an Ethernet switch. I am able to use the printer on Machine A from Machine B.
Another place I volunteer we ran out of ports on our router (max 4), so I used an Ethernet switch to expand one of the router's ports to serve 4 Ethernet devices.
I avoid wireless / WiFi whenever possible because it requires administration, configuration, assignment of a name used by clients, and assignment of a password - if you want any security. A wired (Ethernet) connection has NONE of these challenges.
seacue