I served eight years on my department SWAT team, stepping down last year. As a team leader the last couple of years, I was also responsible for the selection of officers to the team.
One thing you need to understand now is that typically, only the largest of cities have full time teams (cities of say 200,000 or more). The vast majority of deparments have "part time" teams. What this means, is that officers work their regular jobs such as patrol or investigator and then serve on the team as an extra assignment. You train somewhere between 8 to 16 hours a month, depending on departmental budget constraints. You are then on call 24/7 if a hostage/barricade or high risk warrant service comes up. That pager will go off at the most inopportune time. This is exciting for the officer but not particular so for the wife. Being a SWAT officer is about hard work and commitment. It's typically hot or cold in training and on operations. It's repetitive work as it takes many many long hours of practice to hone team movement and shooting skills.
If you want to be a SWAT cop, you need to focus on being a good street cop first. You'll need to garner a reputation as a dependable officer ,one who pulls his weight, never shirks a task, and will be there when things are not fun. This will show you are a team player and selfless, the most important virtue of a SWAT cop in my opinion. At the same time, practice your firearms skills and keep up with procedure so you establish yourself as a good decision maker. If you gain a poor reputation early on, it will follow you for years. Trust me, I've seen it happen.
You don't have to be a body builder but stay in shape. Right now, focus on just becoming a police officer in a jurisdiction that will later provide the opportunity you are looking for. Then, work hard with the patrol officers you are teamed up with. That is the best advice I can give you.