Fundamental coding question: loop, restrications..

Hi.

The more code lines the event editor has the more work the computer has to do. Is this correct? I think more lines need more HD space or RAM. Anyway, it is important for coding that the events are well-structured and do what they are supposed to do, using the easiest, less complicated way.

My question concerns some fundamental coding.
An example:

A game can be played alone or with two players. In the menu I have an event something like this: if mouse clicks on picture "one player" then set variable "#ofplayers?" to 1. If mouse clicks on picture "two players" then set variable "#ofplayers" to 2. Alright.

In a level the events have to look at the actual number of players. If only one player is in the game then...if two players are in the game then...

I use:

if "#ofplayers" = 1 then...
and
if ... = 2 then...

BUT...now my question. LOL
How should such "game facts" (1 or 2 players?) be handled?

Do I have to use
"start of the game" and "#ofplayers" = 1 then...

or just

"if "#ofplayers" = 1 then...

or

"if "#ofplayers" = 1 AND only one action if event loops then..

=====

How does this work? Do I have to use "start of game" for such events? Does it loop and consume unneeded memory with just one line (if #ofplayers 1 then...)?
Do I have to restrict such events?

I am not sure what events should be restricted and what don't have to be.
Of course a line "if number of points > 50 then play sound..." is wrong as this sound is repeated over and over when the player scores 51 points or more. So I have to restrict this event. But what about my example?

Please help me and tell me what events should be restricted.

Thank you very much for your long and helpful comment. :)

"Start of frame" : executed before fadein and called once
>> Fastest

standard condition (like always) : executed after fadein at each loop of the frame
>> Slowest

conditions with "only one action when event loops" : executed after fadein only one time if the state of the condition has not changed since the previous frame
>> Slower than "Start of frame"