Hey there Dark.Knight.
I served. 9 years, Navy + AF. I didn't go into the military knowing I was trans, but I did deal with a lot of depression related to my gender identity while I was in. This may not be true for most folks but for me, the military was actually a tough environment for someone with gender issues. While on some level it strives to equalize the sexes, there are very clear gender demarcations, and try as I might, I was never 'one of the guys.' I have no idea what your goals are for mil. service, but I would suggest thinking about what the highly regulated environment might mean to your dysphoria, if you have any. Also as far as I'm aware, pilots (because of the extra training they get) have an extended commitment...I think 9 years and not the usual 5 (but I didn't commission through rotc so I could be wrong). Just...make sure you do all the homework so you know what you're getting into.
Ok. Fitness. Being in shape is really crucial. I know for rotc they have regular fitness assessments that you do have to be in a semblance of shape for, and these assessments continue throughout your active duty time. I would stress getting comfortable with running above all else. I used to lead fitness assessments and this is by far where the most people have trouble. And frankly the only way you can get in shape to run the assessment fast enough (it's a timed 1.5 mile run) is to run. There are plenty of websites devoted to beginning runners if you are just staring out, and training programs for improving. Runners World has a good site with a forum. Other than that, pushups and situps, and a healthy diet (a lot of fitness forums devote topics to these things). And naturally these things should help you drop pounds over time.
I'm not sure about passing tips...not my forte, lol.
Not sure how useful that was, but welcome!