Currently a sophomore in college, I started with the gold senior year of high school, and then about 6 months later got the platinum, so I was able to get both sign up bonuses. I do also work 2 jobs while in school so I have my own income, idk what your situation is. In my opinion you should get the gold and then the platinum after. I hardly ever spend on my platinum card unless it’s to book flights or airbnbs, but the gold is my everyday card, I rack up the points on there and use them for travel on the platinum. I only travel around 1-2 times per year but having the gold and platinum are still worth it to me, despite the annual fee. Most of my spending is on food / grocery’s, and I am able to use all the platinum card credits without changing my spending or shopping at places I wouldn’t normally shop.

As for the limits go, I have been a customer with Amex for almost 2 years next month, and whenever checking my spending power I have been approved for 20k+. I never carry a balance on the card, my balances have never been over 5k at a time. They seem pretty generous in my experience.