Please help a mom out, specs question.

I’m hoping to get some advice. I’m looking to have a pc built for my 15 year old son. I was originally going to buy a prebuilt one but quickly realized I can get much more bang for my buck by having one built. I have a Micro Center really close to me. I’m not very tech-savvy when it comes to pcs, I’ve only played on consoles. I don’t want to get talked into hardware I don’t need. I don’t have a huge budget, I’d like to keep it $2,000 or less. My son is a gamer, mostly FPS online multiplayer, COD and Rainbow 6 and such.

What specs should I not skimp on? And what type of maintenance am I looking at in the future? How often do you have to update the pc to keep up with the newest games?

I know this is a very broad question, I’m just looking for the most important specs for gaming and longevity.

Thank you in advance.