I'll try to answer your questions.
Using BeerSmith, I assume I would use a Mash Profile of "Single Infusion, xxxx Body, Batch Sparge"? How do I know whether to use Full, Medium, or Light Body?
One way is to look at the style guide and see the description of the beer, to determine Full, Medium or Light Body. Let me give an example.
Let's say that you're making an "English IPA". You go to the Profile Tab and click on Style. It will bring up all of the beer styles. Click once on "English IPA", in the list. Then scroll down and you'll see a description of the style. Look under "Mouthfeel" and you'll find this:
Mouthfeel: Smooth, medium-light to medium-bodied mouthfeel without hop-derived astringency, although moderate to medium-high carbonation can combine to render an overall dry sensation in the presence of malt sweetness.
Light body is a target mash temperature of 148F. Medium body is a target mash temperature of 152F. You would want to target 150F to 152F, depending on your palate and preferences. This is only a guide, so you can target anywhere you want really. I try to stay true to the style though. I prefer a little more body, so I'd probably target 152F.
Do I just match to the beer I am making?
Yes. See above...
Also, it says to "Batch sparge with 2 steps (xxx gal, yyy gal) of xxx F water". So do I pour in xxx gal, let sit for 10 minutes, vorlauf, drain to boil pot and repeat with yyy gal?
This is something that I didn't understand at first. Your goal is to get your mash up to the xxxF specified. It's confusing the way it is in BeerSmith. The way it looks, it makes it look like you add water at that temperature, but in reality, you need to add water much hotter than the temperature specified in BeerSmith, so that you reach the temperature specified. I'll explain how I'd do this.
Let's say that BeerSmith states:
"Batch sparge with 2 steps (.5 gal, 3.75 gal) of 168F water".
I would bring 4.25 gallons of water up to a boil. I'd then stir .5 gallons of that water into my mash. I'd check the temperature at this point. If I was at 168F (I never am at 168, I'm always colder than that!), I'd close the lid and let it sit for 10 minutes. If I was below 168F, I'd lauter and drain some wort off, using the BeerSmith "Infusion" tool, to determine how much to drain off, and bring that to the temperature that BeerSmith suggests and stir it back into the mash. It should settle at 168F. I'd close the lid and let it sit for 10 or 15 minutes, then lauter and drain into my boil kettle.
At this point, my 3.75 gallons of water has probably cooled down to about 185F or so. My grain bed will have also cooled some as I drained my mash tun into my boil kettle. I would then add the 3.75 gallons of water to my mash tun, stir and close the lid. After 15 minutes, I'd then lauter and drain into my boil kettle and start my boil.
I hope you found this helpful.
