Don’t worry about getting bulky, without even looking at you, your body type is more than likely an ectomorph with the dimensions u stated, you can probably eat anything you want and still maintain the weight. Your a hard gainer. You should lift atleast 4-5 days a week and like one-two body parts a day. Eating is also very important with your build in order to gain weight. You need to go on a high carb/high protein diet. This is just a little summary do some research on the internet, there are plenty of articles that will lead you in the right direction.