Yes, you can do it! Let's run your list step-by-step:
Tor's crypto is single core, sadly(until I finally debug and release my patch). So you need - basically - a dual-core CPU. One core to handle the crypto - other to do other stuff. Old Mac and iMac are OK, but be prepared for some complications compiling latest OpenSSL and Libevent on them. Minimal requirement is dual-core CPU + 512M ram. It will handle in no-GUI dedicated mode the single node of Tor fine. I've tested it on Raspberry Pi B+ - it's a singlecore, 512M RAM total, works fine!
Try to use OpenWRT on your router, if possible - it will give you more speed. ADSL speeds are not a hyper-ones, so having 10Mbps down and 2Mbps up does not require much hardware in a stack. If your router can make it - it's fine!
Yes, asymmetric connections like DSL are not a problem at all in running Tor