(1) Well a diagram of your room would be helpful, but the general speaker layout can be found right
here.
(2) Just run a splitter from your receivers subwoofer pre-out to both of your subs inputs. Placement with two subs is actually a rather hard thing to do, but if you do it well you will have great results as the second sub can help flatten your frequency response and give you more SPL.
This will help you place your first subwoofer. Once you have done that, you will need to use your SPL meter, test tones and graph paper to set the second for a better frequency response. If you want to just increase loudness place the second sub on top of or as close as possible to the first.
(3) In general 80Hz is where you would want to set the crossover because that will help reduce the localizability of your sub. To do this I would recommend turning your subwoofers crossover all the way up and relying on your receivers crossover by setting it at 80Hz.
To best set up your speakers I would recommend going to Radioshack and buying a digital or analog SPL meter and then going into your receivers speaker level set and setting all the speakers to the same loudness as this will help keeping speakers from drowning each other out.
Also, a video/audio calibration disc would help as well. I personally use Avia to calibrate my display and it also has many great audio tests that will help you get your speakers set up properly.
