is there such thing as too much protein?

Why are you aiming for that much?? Is there a reason or do you just think that is where you should be?

Too much protein is dependent on your kidney function and training program. The standard recommendation is 0.8 grams per kilogram of body weight for adults. Kids actually need more. People with kidney disease however, should restrict their protein intake to 0.6 grams per kilogram of body weight. There are also recommendations for different types of training programs as follows:
Strength Training, Maintenance--1.2 to 1.4 grams per kilogram body weight
Strength Training, Gaining Muscle Mass--1.6 to 1.7 grams per kilogram body weight
Endurance Training--1.2 to 1.4 grams per kilogram body weight
High Intensity Interval Training--1.4 to 1.7 grams per kilogram of body weight

I say pick your primary type of training and as long as you don't have a kidney issue (including kidney stones), then go with the recommendation for that type of training. Multiply it by your body weight in kilograms (pounds / 2.2) to get total grams. Multiply the grams by 4 to get Calories per gram and divide by your total goal Calories for the day to get the percentage to put into MFP so that it will give you the goal amount you want. Then divide the remaining calories between carbs and fat according to the way you wish to design your program, be it high carb, low carb, low fat, etc.

This is actually a tricky issue...some people need more some need less...it's trial and error. I train 6 days a week, I take in roughly 130-140 grams of protein, that's what my body likes. I've tried lower numbers and I don't like my look. I would say though at 175lbs...and 3 days a week, you would be fine at 100 grams, you don't need to worry so much about protein intake with regards to cardio, it plays a significant role when you're lifting.

My doctor told me I should be eating 300g per day. Since I've lost about 50 lb, he's revised that to 250g per day. But it hasn't hurt me a bit, in fact it's one of the three rules that have allowed me to lose weight for the first time in my life.

A normal, healthy person cannot overdose on protein. Yes, if you already have existing liver or kidney problems, eating too much protein may put strain on them. But it's the same thing for any weak organ you have: strenuous exercise is great for a normal person, but could cause heart failure if you have a weak heart. But for the vast majority of people, there's no problem with eating increased amounts of protein.

Protein is a vital part of the chemical reaction that burns fat (it's roughly three parts fat to one part protein). Protein also repairs and builds your muscles (as well as keeping your hair, nails & skin healthy). So it's better to eat too much than too little. If your body is trying to burn fat, and you don't eat enough protein, it will take those amino acids from your muscles and you will lose muscle mass along with your fat. You don't want that.

If you are trying to lose weight, doctors recommend eating your body weight (in lbs) in protein grams per day. So if you weigh 175 lb, you'd shoot for 175g per day.

If you are not trying to lose weight, but are trying to build muscle or are just strength training or exercising a lot, doctors recommend eating your LEAN body weight in protein grams per day.

If you are simply maintaining your normal daily activities and maintaining your current body weight, you can follow the US RDA guidelines. But most people consider those to be a minimum.

Hope this helps!