How To Mash This Recipe?

I picked up the ingredients for this recipe, as it looks like a decent summer beer. However, I'm a little confused as to the mashing instructions - I've only done two AG recipes so I'm not sure on a few stages of this particular recipe. The instructions are for a 6 gallon batch but say:

"Step-mash: Add 2.25 gal of 54degC water to crushed grains and stabilize to 50-51degC for 30 min. Add 1.25 gallons of 93degC water to bring temp to 65degC; hold there for 90 min. Mash out, sparge, etc."

My confusions are this:

1) The first step of the mash is meant to hold the temp at about 123 F, whereas I thought this is awfully low, isn't it? I thought mashes attempted to hold around the 148-156 F range?

2) The second step of the mash raises the mash temp to 149, and only holds it for 10 minutes. Between the first and second step, will it be enough to be able to convert the starch into sugar?

3) The total water bill for the first two steps is only 3.5 gallons on a 6 gallon batch. I assume the other 2.5 gallons (plus grain absorption and boil off, etc) is to come from the "mash out, sparge, etc." phases. Is there a difference? How hot should the water be for this/these stages, and how should I conduct them?

4) I couldn't acquire the 6-row, so my supplier told me to simply substitute more 2-row. Should I substitute at equal quantities, or is there some sort of adjustment I should make?

Thanks for any help you can offer!

The complete recipe is below:

Ingredients:

4 lbs. American 2-row pale malt
3 lbs American 6-row pale malt (had some sitting around)
3 lbs wheat malt
1/2 cup crystal malt (40L)
1 oz cascade pellets (6.3%AAU)
1/2 ounce Tettneng pellets -flavor-(4.5%AAU)
Grated lemon peel from 2 lemons (do *not* use the bitter white pith)
Juice from 2 lemons
Wyeast 1056 500ml starter

Procedure:
Step-mash: Add 2.25 gal of 54degC water to crushed grains and stabilize to 50-51degC for 30 min. Add 1.25 gallons of 93degC water to bring temp to 65degC; hold there for 90 min. Mash out, sparge, etc.

Bring wort to a boil and add Cascade hops. After 30 min, add 1/2 ounce tettnang hops, lemon peel, and lemon juice. Boil for another 30 min or so until volume is about 6 gallons. Chill wort, put into fermenter, let trub settle out for a few hours, transfer clear wort to a sanitized glass carboy, and pitch yeast.

OG= 1.052 (for a lighter beer, bring volume to six gallons)

When bottling, add 3/4 cup corn sugar and juice and zest from 2 lemons.
Submitted by: Anonymous

1. This is for a protein rest. You can skip that temp rest if you want.

2. Skip this rest also and just do a single infusion mash around 152-154F for this beer and you will be fine.

3. Figure 1.25 qts per pound of grain for your mash and then enough sparge water to get your volume minus grain absorption.

4. You want to use 2-row. You can just sub it out equal basis.

If you want to do all grain brewing, I would recommend that you get Beersmith brewing software. It does all of these calculations for you and then you can just print out a brewday sheet to go by. Best investment you will ever make for AG brewing.