Four buttons are standard for a formal suit jacket sleeve while a casual jacket usually has only one.
One sleeve button is casual, four buttons are formal. The number of buttons is usually according to when, and to what occasion(s), you will use the suit. Regarding the space between the buttons, a general rule is that the buttons should touch each other.
Suit jackets are formal statements. Everything about them needs to be adjusted in order to complement the dress code. A formal suit jacket has 4 buttons on the sleeve conventionally. A casual suit jacket has only one button on the sleeve. Sleeve buttons don’t actually have a function. This is why many such suits just have fake holes as they look much better. Another important thing is the gap.
All 4 buttons on the sleeve should be touching. However, care should be taken to prevent any overlap. However, people often place the buttons according to their own preference. Some choose to have gaps whereas others overlap.