私は猫舌なので、いい感じに熱い温度のコーヒーをくださいって英語でなんて言うの？

All three expressions are suitable for this situation.

My tongue is very sensitive. Please don't make it too hot.

Asking for extra milk will reduce the temperature of your coffee. However if you are like me and do not like milk, this won't work for you.
In this case I would say: Do you mind not making it too hot?

Example:
Can I have a black coffee please? And do you mind not making it too hot.
-This simply says that you do not want the temperature to be too hot.

May I have a warm coffee please?
-Warm implies that you don't want it to be boiling hot.

May I have some coffee please?Please don't make it to hot.
-This expression is very clear as it lets your listener know what your preference is.

*Alternatively ,if the coffee is hot you could request some cold milk on the side eg.May I have a cup of coffee and some cold milk on the side ,please?

1. If you like coffee with milk, then the answer is to ask for cold milk with your black coffee.
2. Piping hot = (of food or liquids) very hot.
   "The crust was piping hot and I couldn't eat it"
   (To go) easy on something = to not take or use too much of something:
   "The doctor told me to go easy on the spicy food for a while."

This means that you want coffee but bit very hot. You can also ask with cold milk so that the coffee is not too hot.