Some tips:
Do a full volume boil. Do not top off. A smaller batch of IPA that was not topped off will always be the better beer when compared to a larger batch of IPA which was topped off.
With that said, I would shoot for about a 4.25 gallon boil and 3.4 gallon batch.
Mash the following in a grain bag around 148-150 F for 60 minutes:
2 lbs. 2-row
1 lb. wheat
1/2 lb. carastan (1 lb. may be too sweet [it will for me at least])
Mash with 1.25 to 1.50 liters water per lb. of grain
...plain tap water will do just fine
Afterward, dunk the grain bag several times in your 5 gallon brewpot, which contains approx. 3 gallons of 170 F plain water. The grains will be rinsed and conversion will stop. Let the bag drip out, but do not squeeze it. Place it in a bowl to let the rest drip out so you can add it later.
Meanwhile, add the grain wort to the plain water. The boil volume at that point should be 4.25 gallons level. Bring to a boil, and add 2 lbs. of LME or DME. You will be at the 60 minute mark in your boil, so add 1/2 oz. Apollo hops and boil this for 45 minutes until you make your next addition at 15 minutes left in the boil. At this point, add your irish moss/whirlfloc, yeast nutrient, second hop addition of 1 oz Cascade and 1 oz. Chinook. Boil for another 10 minutes, add 1.5 lbs. more LME or DME, about 1/2 to 3/4 lb. of corn sugar, and another ounce of Cascade. Skip the 30 minute addition entirely for this beer. It won't give you flavor, just more bitterness which you don't necessarily need.
During the last minute of the boil, place the lid on the kettle. Quickly cool your wort via an ice bath in your sink. You'll need a crapload of ice and cold water. After about 10 minutes of cooling via this method, dump in an ounce of Amarillo and 1/2 oz. Apollo and 1/2 ounce Chinook. Quickly cover and bring down to 68 F. Test the gravity; it should be around 1.065-1.070 OG. Aerate your wort and add your yeast (preferably a WLP001 or 1056 yeast starter). Let ferment and condition for 3 weeks at 65 F before you add your dryhop, consisting of 1 oz. Amarillo, 1/2 oz. Apollo, and 1/2 oz. Chinook, and 1/2 oz. Cascade. Dryhop for another 7 days at 68 F before bottling with priming sugar and waiting 2-1/2 weeks at 72 F.