Questions about flying for the first time by myself

Hi i'm flying for the first time by myself and i have a lot of questions. For reference i'm flying from dayton ohio to charlotte nc, having a 1 hour and 18 minute layover then flying to Greenville sc. I'm flying with American Airlines and the connection is on the same ticket

1. i know its best to check in online before getting there but i have to check a bag so how will that work

2. will my checked bag be moved to the connecting flight or will i have to get my bag

3. i'm a little worried about the layover cause it seems a little short is that going to be an issue and if it is how do i ensure i get off the plane as quick as possible

4. for American Airlines do i choose my seat in advance; on the website it looks a little confusing

5. once i check in online and figure out my gate is there away to figure out where my gates are before I get to the airport

Answering any of these questions would be sooo helpful, thank you so much!!