As someone who's helped a few folks at this, here's some advice.
Apply ASAP. If you have a DAL or FEDEX app on file for 2 years and you update it, you A) won't miss a window when it closes without notice and B) send a signal you've been interested a long time (i.e...I didn't just apply because SWA turned me down)
Second--FEX written expires in 2 years. Shoot for 18-12 months out to take it. If you make less than 90% consider taking it again.
737 types are expensive and the BRAND you as a SWA wannbe. So--if your blood in canyon blue, and you are 100% that's your first choice--go for it. If you think you might want a shot at Airtran, CAL, Delta, or UPS...realize what the type says to the interviewer. With lots of folks leaving carrier X for carrier Y, the cost of losing employees does factor into the decision process. Make your own call, but if you are connected it seems you can get a SWA interview without the type. BTW...they probably won't be hiring for a year anyway, so why burn those bridges and that money now. If they open up you can get your type at Pan Am, FTI, Highter Power, K&S, etc in about 2-3 months max. No major incentive to do that early, IMHO.
And the most important tip of all:
Don't be a dirtbag at work. If you work hard until the last day, you can always stay in IF there is another 9/11, or things in the industry change rapidly, or you change your mind. I've seen several guys who I thought were 100% sure they were bailing change their minds, and stick around. So--don't burn bridges. Doing a good job there will also make you more marketable to a Guard or Reserve job--if you want to play that card. (I certainly enjoyed my job flying Eagles part time, and thought it made a huge difference in my financial situation those first couple years--as well as being very enjoyable for a lot of other reasons).
Network network network. Can't stress that enough.
PM if I can be of any help, and best of luck...