I am just starting Seasonale myself, after 18 months with a copper IUD. Prior to this I spent 5 years on pills, 3 years on Depo, and another 3 years on pills, followed by a year of abstaining.
I am not expecting any problems with the Seasonale- the type and amount of horomone dosage is very similar to Ortho-Cyclen 1/35, the pill I always took.
In addition, I used to take 4 packs of active pills in a row and only get my period 4X a year. This can be done with any monophasic pill, cost comparison in this way puts Seasonale waay cheaper. Even when all (28) pills are taken month by month, Seasonale is still cheaper (if paying out of pocket). You can price BCPs online (there are reputable online US pharmacies competitive with your local ones) and your local drugstores should also be able to provide you pricing info over the phone.
Seasonale comes packaged 91 pills at a time, 12 weeks of pink active and 1 week of white inactive. Your public health provider should most likely have these pills, and your regular gyne might even be able to provide you with a free sample.
All horomones are steroids, and progesterone (and synthetics) will cause an increase in appetite, accounting for one reason why so many women gain weight with depo and many pills. With respect to this and a healthy lifestyle, if you are able to use BCPs you should be able to find one that works for you while avoiding unpleasant side effects that may come with it.