Quoting someone else on HBT, KISS. Keep it stupid simple. You are making beer, not a soufle. Heat the water somewhere between 158 and 162. I never could make the heat quit to get my strike temp to 161.1, my thermometer won't even read that close and I can really only measure the amount of water between 4 1/2 and 4 3/4. OH, by the way, if your pot is 5 gallons and you put in 4 1/2 gallons of water and add the grains, it will run over. Reduce your recipe size to 2 1/2 gallons and it will work out.
Stir in the grains, I mean really stir them in so you don't have any clumps. If your grain is crushed really fine, you don't need 60 minutes to mash, I've been giving mine 30 with good results but for this time the 60 would be good. Mash out? Why? You pull the bag of grains out when the mash is done and turn the heat back on. Your wort will reach mashout temp in minutes and continue on to boil. The enzymes will give up way before the boil.
Let your bag of grains drain and keep adding that liquid back to the boil pot. Squeeze it out, like really squeeze it out. It owes you. Now look at how much wort you have in the boil pot. Not enough? Add the amount you need to the bag of grains, stir it in a bit and squeeze it out again. 4.31 gallons? How about 3 1/2 to 4 gallons. Much easier to guess. It will still make beer and if you crushed you grains really fine and rinsed out as much sugar as you can, you will probably be pretty close to the predicted OG if you are at 4.
Watch the pot when it approaches boil, like really watch it with your right hand on the heat control and a spray bottle of water in the other and be ready to use both at once. If you have never done all grain before you will be shocked at how much hot break material you get and how quickly it will boil over.
Start now looking for a bigger pot than the 5 gallon one you have. Once you find out how simple BIAB really is you are going to want to do some 5 gallong batches too. I use a turkey fryer (7 1/2 gallons) but I have to watch my quantities carefully so I don't over flow it. Pretty hard to make a big beer in that size pot too so if you decide you want to try an imperial or barleywine, get the bigger pot. I'd suggest you look for a 10 gallon.