Welcome to the forum,
Your most immediate concern is that Anti androgens will kill your libido.
"The pill" is estrogen based, it is not an anti androgen. Yes, estrogen introduced into a masculine body will eventually lower testosterone, how much I cannot say for sure (YMMV). Or your mileage may vary.
I've only been on low dose anti androgen for two weeks and my libido has dropped quite a bit

Your ability to get an erection will become more difficult on anti androgens. Your ability to climax may also suffer as well. Some trans women cannot get erections, and some can still get them after years of hrt. But it still will be difficult to get them.
After a prolonged period of time on anti androgens you may grow breasts, and have female nipple development. If your testosterone is too low, you may eventually get osteoporosis (weakening of the bones). Low testosterone will also inevitably cause sterility.
Anti androgens slow hair growth, they do not create female pattern body hair. Only estrogen can do that.
There is more information on the wiki here at Susan's, either under Spironolactone, Cyproterone Acetate, and/or anti androgens...if you wish to do more research. (I would post the links, but I'm on an iPod)
As you can tell...hormones are serious business. Weigh the risks and rewards for your own needs. I have not listed all of the risks/effects, but I urge you to do some serious research if you are seriously considering this as an option.
(I'm posting this at the risk of sounding b*tchy, but that is not my intent, just my tone of voice)
-Skye