1:Unity is a great engine to begin with but you should know how to code in order to make a game in it, TripleA games means the game like God of war or Gta etc games which needs a lot of people and money,
2:Remember you are making a game from scratch so everything you have to create from your own, so a game like super meat boy is not easy to make nearly impossible for your first game
3: your first game should be simple and small honestly my first 2d game was a man killing monsters and getting a high score.
4: if you know how to code then unity is good if not scirra construct 2 is good for small games and requires no or little coding (depends) i too made my first game in construct2, there are some more engines which doesn't require coding like game maker, build box, game salad.
5: my opinion would be aim small try to make your game in a month or two if it takes more than that you need to make it more simple, divide your work into small parts and if you dont know coding try to learn the basic atleast , so you can do simple coding
Good luck hope it helps