Make "Match 3" layout start without any preexisting pairs

I'm trying to figure out how a match 3/"bejeweled" game works. I have 25 black squares that act as squares on the game grid that spawn one of 3 random colored squares. If a square is touching another square of the same color, it is is suppose to add a point of which when equals 3 or greater would then be destroyed giving the player points. I have no actual gameplay done as I am first trying to make the grid layout start with 25 random squares to start with. My problem is that I cannot figure out:

1. How to prevent sets of 3 or more vertical/horizontal from generating at the start of the layout.

2. How to make all squares associated with the 3 or more pair be destroyed once in the pair.

I am including my .capx file as well as a screeenshot of my events

drive.google.com/file/d/1dBMcFClfj7bHHmk_3812z0i5becWXLSz/view

Thank you.

I don't understand what's going on in your code, and sprite names like "P1" and "G2" don't help..

Have you seen this tutorial?

gamedevelopment.tutsplus.com/series/make-a-match-3-game-in-construct-2--gamedev-12721

It explains in great detail how to make a match 3 game.

P1 refers to the black square that gems randomly spawn on and G1,2, and 3 refer to the three different gems. I'll look into the tutorial to see if it helps break it down though.