[marcus_in_absentia]

Just to add something on what the previous two have answered for your first question, what I've learnt is that you CAN fake the doubling effect with only one take. What I do when I'm pressed for time is take the single track and pan it hard left. I then make a copy of it and pan it hard right, changing the EQ and (MOST IMPORTANT PART) add a 1ms delay. Not DELAY as in the effect, but literally delaying your entire track by 1ms (or an even smaller/larger fraction, experiment with it). This separates both tracks to give the impression of a second recording, when you're actually using the exact same track.

As for panning solos, you don't necessarily have to pan dead center. I like to pan it 10% either to the left or the right (to recreate somewhat the context of a stage). As for harmonized leads, you can opt for a bigger pan to separate the tracks, maybe 20% left for one lead, and 20% right for the other. Do make sure that both lead tones are COMPLEMENTARY, and not identical.

You can even go crazy and double track your leads as well (Randy Rhoads did it), and even quadruple track your rhythm parts (Porcupine Tree's Blackest Eyes is a result of many many layers of rhythm guitar).

Also, do note that while your choice of mic is important, your preamp and DAW is MORE important (kinda like how the amp makes up a bigger part of your tone than your guitar). You get what you pay for when it comes to preamps. I'd stay away from USB preamps and invest instead in a nice firewire preamp. The PreSonus Fire Studio is great at it's price point, and a DAW like Logic is great as well. Both would work splendidly with an SM57.

Hope all this helps. (Your mileage may vary).