Jumping off of the mash temps thread, I don't OCD about the temp anymore. I used to think I was ruining a beer when it was off a few degrees... (it doesn't) I just get into range. Low/mid/high. Very good points already made by others, it's all about dialing your setup in. It takes time and sometimes no matter what s*** happens.
Do not OCD about mash thickness either. I use 1.6qts/lb because it usually results in simple volumes of water that are nearly equal to sparge (IE 10lbs is an even 4G) This is important for instance if there is a zombie apocalypse and you are without means to measure accurately. Incidentally, a Cleveland Indians beer pitcher circa late 90's holds exactly 2lbs of grain... Another method is to buy a nice wooden brewing spoon and add measured amounts of water in kettle (I used gallons) and immerse spoon take out and use a saw to add a band to water level. I also added a double band for 5.5G as it is my intended batch size and use the spoon to assess boil off rate.
While I agree pH is important and it can wait until you get your process sound, you should at least be mindful of your water. Do a little research. Find if your water is treated with chlorine or chloramines. These will give your beer off flavors. Pretty easy to treat with campden tabs.
PS you owe your buddy a beer for the suggestion to reheat (we've all done it) Congrats on your first step mash!