Iīve been told by several Doms the beginning was very hard for them, which makes sense, as guys get taught from early on it is not ok to hit a woman or be violent with her.

I have also been told it gets easier with time, namely when it becomes apparent how much the sub likes it and how happy it makes her.
Encourage your sub to give you feedback - both positive and negative.
Doms are not mind-readers and should not be expected to be, either.

I am with Oz on the safeword issue. It is always good to have that as a fallback, though a good Dom will learn to judge his subīs reactions and limits on his own accord - again, it takes time.

Also, it might happen at some point in time (with me, it did happen more than once), that the sub is not using her safeword and thinks she can go further, but the Doms breaks off the scene because he knows better (I only realized after the endorphines had worn off that to keep going would have been a bad idea).

However, that should not worry you at this point in time - take slow steps in the beginning, you will get more comfortable that way than rushing into anything and doing serious harm.

I am a sub myself and have no switch tendencies; however, I like to talk and learn and also understand what happens inside a Dom, and if I feel I could contribute something helpful, I will do so.

Good luck for the two of you.