I've not done track before, but I've been swimming a very long time. What I can tell you about swimming is that it will take up a ton of time if you want to get good at it. It's a very perishable skill meaning if you get good and even skip a day or two you will really notice it. At my competitive peak I was swimming about 2.5 hours in the morning, 2.5 hours in the afternoon, lifting weights 3 times a week for about an hour each session. The morning and afternoon swimming workouts were 7 days a week. That is a HUGE time commitment as I was still in school at the time. It can take a few years before you get good at it. All of that sounds pretty bad, but I will also say that it was one of the best things I ever did. All of my best friends were swimmers and they still are years later. Health wise it's a great sport to undertake, it won't destroy your knees although it can be rough on the shoulders. There's my two cents on it. Hope that helps.
Any legitimate sports team you join while require a lot of time (practicing, traveling, and competing)
Might want to try joining a club for a sport that you're interested in
Yes
Whichever one you want to do just do it. Track is in the spring anyways and swim is during Winter so why not both?
Your a girl so do swim... If you know what I mean :)