Okay, time to take a deep breath. Cheesemaking isn't rocket science, but it is science, with a lot of artistry thrown in. Slow down, look at your technique (accuracy is very important until you get it down), and stick with one variety of cheese until it comes out as expected. all the gadgets in the world won't make good cheese if you don't follow the basic "rules" of cheesemaking - time, temperature, acidity, coagulation, etc. So, I have a few questions and suggestions that might help you.
1) You frequently mention overshooting your target temp...are you using a hot water bath to warm the milk or is it directly on the stovetop? A hot water bath is much easier to control, especially if you also monitor the temperature of the water in the outer jacket - it should be 5-10 degrees hotter than you want your milk/cheese to end up.
2) Milk should NOT be stirred for more than 30 seconds after adding the rennet! As soon as the rennet hits the milk, coagulation starts so you don't want to stir long, just thoroughly. I use a skimmer to stir around the pot a couple of times, up and down a couple of times, then insert the skimmer straight up and down in the milk to slow the movement of the milk as soon as possible.
3) how are you diluting your rennet? No matter the type (tablet, powder, liquid) or variety (animal vs vegetable), it should always be diluted in 1/4 cup cool non-chlorinated water JUST before adding it to the milk. If liquid or tablet, stir the rennet in the water until you don't see the particles anymore.