nope, router is not necessary, you can use cheap switch if your ISP gives you several IP addresses (or you use it just for LAN). And, even if they don't you could start socks proxy on one that has been given IP from ISP (running 24/7).
I have used A1200 with 10Mbit pcmcia and 8port switch and got about 200kbyte/s when using smbfs for transferring files to PC. (IIRC its a little bit faster in opposite direction).
Just be sure to TURN OFF firewall in Miami, cause it will slow down drastically everything.
