First partial mash brew...please critique

Actually my first brew period Im looking to brew an ESB. Here is my recipe.

[size=+2]Güden ESB[/size]
[size=+1]8-C Extra Special/Strong Bitter (English Pale Ale)[/size]



Size: 5 gal
Efficiency: 65.0%
Attenuation: 74.0%
Calories: 193.89 per 12 fl oz

Original Gravity: 1.058 (1.048 - 1.060)
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Terminal Gravity: 1.015 (1.010 - 1.016)
|=====================#==========|
Color: 13.7 (6.0 - 18.0)
|==================#=============|
Alcohol: 5.64% (4.6% - 6.2%)
|==================#=============|
Bitterness: 44.56 (30.0 - 50.0)
|===================#============|

[size=+1]Ingredients:[/size]
4.0 lbs Maris Otter
0.5 lbs Victory® Malt
0.5 lbs Special Roast Malt
4 lbs Dry Amber
.5 oz Target (10.0%) - added during boil, boiled 60 min
1 oz Challenger (8.0%) - added during boil, boiled 30 min
.5 oz Fuggle (4.75%) - added during boil, boiled 15 min
1 ea WYeast 1275 Thames Valley Ale


A couple of questions I had as well if anybody can help me out. I'm doing the partial mash in a 3 gallon cooler. It has a false bottom. Should I bring the water up to temp, put it in the cooler and then add the grains? Also, regarding efficiency, I kind of just guessed 65%. Im sure I will get a better estimation when I do my first brew. Is that too high of an estimation for a noob like myself? Im planning on doing a single infusion mash. I might drain a few quarts out after mash is complete, bring that to a boil, and then add that back into the tun for a mash-out...then drain and sparge. Planning on mashing in with 6 quarts of water and sparging with 6 quarts leaving me with roughly 3 gallons total to boil.

Any help is greatly appreciated.

Thanks,
billpa

Heat the water to about 180F, put it in the cooler for 20 minutes. Adjust to strike temp if necessary & add grains.

You'll need about 8 quarts for sparging, because you'll lose some of the first running to the grain.

65% is a good place to start.

65% efficiency is realistic. I get about 60% + and I don't really sparge very well using the mesh bag method of Homer Simpson Mashing. Just don't forget to add a little Irish Moss. The recipe sounds very tasty...I have never used grains made from Otters (hair might be a problem), but I have used the Victory malt with plain old 2-row with great success.

Thanks alot for your suggestions guys. I will let you know how it turns out!