Never rented a car before - need advice?

Hi all, I have to rent a car in about a week through Enterprise. I have never rented a car before (I'm 25) and wasn't sure if someone could provide me some guidance??? Sorry if I sound silly but traveling (especially by plane) gives me a bit of anxiety and I just found out that the person that we are staying with sold their second vehicle that we were planning to use during our stay so this was an unexpected cost.

• Can I add an additional driver? The additional driver would be 24. How does that process work?

• Do you have to pick up your car at the time you choose on the app?? Our plane is landing after midnight and 11:30 is the last available time slot. We are staying about 15 minutes from the airport and we were just going to come back the next morning to pick it up. Wasn't sure if they were super rigid on time? I obviously know to have it back by the drop off time but wasn't sure about pick up.

• Do I need to provide my insurance card?

• What is the difference between a standard and a midsize car?

Any other additional tips are welcome. Especially when it comes to the damage waiver and such. Thank you!