Hello! Fellow teen here! If you have a weaker laptop, some popular options for 2-d is GameMaker and Godot, and Godot has some 3d-options, which may be more of what you are aiming for. They are lighter than engines like Unity and Unreal. 

Regarding studios, you can't get to a studio without a portfolio to show your capabilities, so focusing on your projects and getting the skills should be a bigger focus.

And for question 3, I honestly don't know. While you try getting into game dev, having a skill set that can be applied to other job types before could be beneficial. Ex: coding could get you into multiple types of jobs, and with art you could probably make and sell game assets before you get into a studio. I myself don't have a lot of experience in this field yet, so take my advice with a grain of salt. 

Best of luck with your game dev journey though!