Let me see if utorrent is out for mac. If so use it, its a GREAT client. Ill BRB.
http://www.utorrent.com/downloads/mac <--- light, small, fast and easy to set up. At least the windows version is, I take it the mac is the same. BTW when it is asking for you to input your speed, all it is going to do is determine your upload settings. Always make sure your download settings are "unlimited" under preferences. If you need it throttled back, you can do so temp. but always take it back to unlim. Upload is different, you want it set to about 20% of your rated upload speed. If you are not browsing the net or you are just using BT then set it to 90 of your cap.
Ok now for your questions. Ill see if I can answer them in one sec. Im at work so I am here and there.
Utorrent will forward your ports for you and basically walk you through step by step.
http://www.matisse.net/bitcalc/
This might help to. Try it out, let me know any questions you might have. I wrote a step by step guide for testmy but that was years ago. It is in the guides section but is horribly outdated, I wouldnt recommend reading it. Im sure you know by know the first rule of BT is patience. It usually takes it a while to hit speed.