first, are you going through a breeder? if so, what breed are you looking at? if you go with a responsible breeder (the only kind that you should ever purchase from), they may be able to meet your preference for a particular gender but they will match you to the dog that best fits your personality and needs.
if you are going to get a rescue dog, is there a particular breed or mix of breeds that you plan to look for?
I much prefer males. In my breed, getting 2 puppies so close together is a recipe for disaster, especially if you aren't an incredibly experienced dog home. Even though they will be a year apart in age, littermate syndrome is one of the things you'll have to consider. blog.betternaturedogtraining.com/2013/07/18/littermate-syndrome/
the rule of thumb for adding a second dog is: first dog should be fully mature (for medium and large breeds that means at least 2-3 years old). first dog should be fully trained and have no bad habits that you plan to work on. have a plan in place in case, once both are fully grown, they don't like each other.