First I'd like to point out that if you want to get a male for sure you should probably get an older frog so you can guarantee that it's a male. With babies it's quite difficult to tell so it'll be a 50/50 shot of getting a male.

Your frog will probably eat more and more as it grows. When it's growing, a good rule that a lot of people use is to feed the frog as much as it will eat in 10-15 minutes. Stick to either crickets or earthworms/nightcrawlers as a staple food source (no wild caught and NO red wriggler worms). As an adult your frog will be eating a substantial amount of food; like, a lot. It needs to maintain a large body weight. In this case you just have to do trial and error to maintain his/her weight. Feed enough so that the frog stays nice and plump but be careful not to feed so much that it becomes overweight.

It usually takes a little over a year for a juvenile to grow into an adult. Sometimes longer, sometimes short. Depends how much it eats, how often, the quality and nutritional value of the food, and stress levels

if you are going to get a juvenile i would suggest getting some crittee keepers or plastic tubs and work your way up to the 55 gallon.

Any crickets that are about the length of the space between the frogs eyes are ok to feed

it's up to you with the cover. Glass tops keep in moisture better but screen tops have better air circulation. With a screen top you may struggle to keep uo humidity and with a glass top you have to clean regularly to prevent the growth of bacteria.

good luck!