"You can't make good cheese from bad milk."
But you can make eatable cheese from drinkable milk. I've been using store bought P/H since I started making cheese last September, about 40-45 cheeses so far. A half dozen of those were with real milk, and they were memorable. P/H milk is harder to work with, and can convince you that you don't want to make cheese; but if you persist you can gain the experience that only comes with the repetition of the process. My current practice is to use 1 gallon of raw Jersey milk to 3 gallons of a local dairy's P/H milk; this is strictly because money is quite short at present. It's making a tolerable good cheese. Use real milk at least once at first, so that you can experience what real curd feels like. Then make a bunch of quick ripening cheeses, like Caerphilly or Lancashire from the store bought milk, and make a lot of Welsh Rarebit and macaroni and cheese.
Here's what I do for P/H milk:
Adding calcium chloride in about the same amount as your rennet will give you a stronger curd. Heating the milk just a couple of degrees hotter initially when you add the rennet will help. Some brands of milk are handled more gently than others, and give a better curd, so try all your local brands. When you cut the curd, do the cross cuts first and let it rest a couple of minutes until whey starts coming out, then do your horizontal cuts. Work very gently. When first stirring, use the narrow handle of your ladle, and just gently nudge the curd until it starts to firm up. As the curd starts to shrink, it will firm up, and you can start using your ladle to lift the curd from the bottom to the top; as it firms and shrinks more, you can actually stir it back and forth. The biggest problem that I've found with cheap milk is that hte fat has been damaged enough that it easily forms short chain fatty acids (think Parmesan) that give the cheese a lot of sharpness. I go for cheeses that have a long pre-ripening time, where the extra time ripening with mesophilic bacterias help to give the milk some of the character that it was lacking.
Making quick ripening cheeses let me see where I was going astray with handling the curd too roughly and letting the acidity get away from me.
Also, chevre is real easy to make and really popular, so you can always make that when you don't want to make a pressed cheese. Wish I had access to goat's milk like that!
Dave in CT