1st ag questions

So I am going to make my first ag brew sometime this week and have a few questions. I am going to be making biermunchers swmbo slayer.

So I entered the recipe into beersmith and it says that I should mash with 15.38qts(1.5qts/lb of grain) of 164F water to get a mash of 154F. How does it know what temp the water should be without knowing the temp of the grains? Is there somewhere I can enter the grain temp so it could adjust the water temp, or does it always assume some constant temp for the grains?

For the first sparge it says to use 1.94gal of 168F water and for the second sparge it says the same. Can I just sparge once with 3.88gals(I want a 6.25gal preboil volume of 168F? Would it just lower my efficiency or would there be other drawbacks to not sparging 2x? Also, how long do I have to let the mash sit after adding each sparge and stirring?

Is there a formula that I can use that would use the amount of wort I got from the original mash that would then let me know how much sparge water to use in order to get my preboil volume? Also, a formula that would let me know what temp of water to use if I wanted to do a 170F mash out?

Thanks for any help you can give.

Beersmith rocks. Take some time to play with it. You will see that you can enter the temp of your equipment and ingredients and also the type.

Set the temp of the grain to 70 (or whatever you ambient temp is) and the temp of your cooler to what it is (I highly suggest you pour in a gallon or two of very hot water and splash it around and let it sit for a bit. This preheating will help limit the amount of temp drop you get when you add the grains) Set the temp of the cooler to the temp your preheat water is just before you pour it out.

Once beersmith knows the quantity and temps of this stuff, it can tell you to a degree what your mashing temp will be. I literally hit the exact temp I was shooting for (it turned out to be too high for my first batch, but at least I hit it exactly!)

There are settings for size and shape/type of cooler IIRC and everything.

It will also tell you how long to mash for. Not sparging enough will result in a lack of efficiency, and a smaller volume in the kettle. Beersmith will literally tell you everything you need to know, you just have to figure out how to read it.

Ok, I will have to play around with beersmith a lot more. 1 other question - Do I need to take a gravity reading for each of the mash run offs, or just for the first one, or no need to take it until after the boil and it has cooled?

I take mine pre and post boil