Trying first partial mash -English Bitter -help with recipe

Hey Guys,
I've been brewing for a long time (since 1990) but I've never done a partial mash brew. This time I'm going to try it and need help with the recipe. I'm shooting for an English Bitter similar to Ruddles County This is what I've got so far:

Amount: 5 gals

Malt:
3 lbs Muntons Pale Malt
3 lbs Muntons Extra Light Dry Malt Extract
1 lb 40 L Crystal Malt

Hops:
2 oz. Bramling Cross (5 AAU X 2 = 10AAU) 60 minutes
.5 oz Bramling Cross 15 minutes
.5 z Bramling Cross 2 minutes

Yeast: Wyeast 1028 London Ale

I'm thinking the initial SG will be around 1.036, 5 lbs of Munton's extra light DME plus 1 lb Crystal gave me 1.042 last brew, and this will probably be the equivalent of 4.5 lbs of DME, I'm assuming. My goal is a light, hoppy and malty bitter of around 3.5% ABV.

My big question is about the mashing stage: I was planning to do a single step infusion at around 156F for 30 minutes (does this sound right?). To hit this temp I was thinking of bringing 1.5 gallon of water to 170F and adding this to the 4 lbs of malt (crystal and pale). Would this get me near 156, if 156 is a good goal?

I'm pretty excited to try this -next is ALL GRAIN! with pretty much the same beer goals, so I can compare results.

Thanks for any feedback you might give.

-Aaron

I would aim for 152F and give the mash an hour. At 156F the wort would be relatively low in fermentable sugars.

Thanks David, in that case I'll reduce the strike water to 1 gallon to shoot for 152F. Anyone else have any input on this recipe? Much appreciated.

-Aaron

You'll need at least 5 quarts of water for the mash, six would be better. I'd start with 5 quarts at 170F and have a quart of boiling water and one of cool water handy to make the final adjustment.