Do I get to board on plane first?

You'll be the 45th person to board. However, chances are some of the earlier people won't show up on time and some low numbers are reserved for elite travelers and may not get used. But it's good you'll get a window seat if that's what you want.

Southwest has a page dedicated to the boarding process
https://www.southwest.com/html/travel-experience/boarding-your-flight/

You're A groups, so you should be able to pick and aisle or window seat without problem.

Southwest does not assign seats, you are assigned a boarding order. They break them up into 3 groups (A,B,C). A Group is boarded first, so you are the 45th person to board the flight.

This is a very good position and you should be able to have a pretty good choice of seats enabling you to choose either an Aisle, or Window seat.

Seriously does it really matter when you board the plane? I'm fine as long as I don't miss my flight. I'd rather wait to be last to be honest with you. The less time for me on a plane the better. I hate flying!

No, you do not get to board first.

You are in the first boarding group (ABC), so that is good. You are toward the end of that group, but you should still have a good selection of seats when you board.

Yes, that is good..it means you will board the plane with the first group. Be sure to be at the boarding gate on time or your assigned order will make no difference.

On Southwest, there's no reserved seating. The A group boards first, and you'll be the 45th person to board.

Firstly, I don't fly Southwest. Secondly, why worry if it's a good seat or not? Be happy your in a seat.

No you will NOT board first. Have you been on an aircraft before? You most airlines have a seating map

A45 is towards the back, so they will probably call you among the first.
EDIT. So, not only are Americans illiterate, they don't even stick to normal airline conventions! Besides, A45 and 45A would be the same seat if you think intelligently about it!!!!!!!!!

first group to board yes, not first person to board

Ok.