Different distance between the text

Hi,
I have several problems with my text distance. All settings are default except on the theme syling options > Advanced Styling. There I put 1.2em as Line Hight for H3 and H5. I had to do this changes because otherwise the space between the text lines were to small:

Here is the example

My problems:

1.If I press “ENTER” between my Heading 3 and Heading 5 there isn’t a normal “ENTER” distance if I write an text and put there “ENTER”
If I press “ENTER” twice after my Heading 3 I am getting a too big distance between H3 and H5
How can I change this so that I have a normal distance between H3 and H5 like in paragraph.

2.Can someone tell me the difference of the following
2.1. Strg + Enter =
…im my screenshot I think this is a little bit more distance as in a normal text
2.2. Shift + Enter = New line without distance
2.3. Enter = ?

3. What is the difference in html between an empty line and ” “?