Shalom. I have a question about the original letters in the Torah, which letters did Moshe used to write the Torah? And the other thing is, what do we know about the closes pronunciation to the supreme name Hashem (YHWH), which is the most accurate.

The Torah was written in the same letters we use today. The closes pronunciation of the supreme name is as is printed in the Siddur. Nowadays, we do not pronounce as is written we only say "A-donai" wherever it is supposed to be said. We have in our minds the name. Rabbi Yitzchak Grinblat