A calorie surplus is the most important thing, although there's no point having a huge surplus because you'll just get fat quickly (muscle growth is very slow compared to say, how fast one can reduce body fat). At least 200 calories above whatever intake maintains your weight is a good place to start. You can lose weight fast without muscle loss in most cases, but you can't gain weight fast and it not be mostly fat.
Protein powder is just food - think of it as essentially powdered milk - typically non-vegetarian/vegan powders are either casein or whey (remember Little Ms. Muffet eating her curds and...). Some powders have added calories from sugars etc although these are usually labelled as 'gainer' or meal-replacement shakes.
No. Calories are a measure of energy. All foods are made up of either protein (4 calories per gram), carbohydrates (4 calories per gram), or fat (9 calories per gram). Alcohol is sort of a 4th (7 calories per gram). How the percentage of your calories is divided between protein/carbs/fat is less important than the overall calories you're eating, but is still important in the sense that it can have effects on health, hunger, recovery etc. I would suggest going to somewhere like RippedBody.com (ignore the name) and
reading the nutrition guide on there since it'll give you the hows and whys.
Assuming you had a good, wholesome and varied diet, it's not that hard to add a few hundred cals from any number of things, most of it is going to come down to preference and if you find you can easily eat a higher volume of food, or find that hard and have to resort to things like liquid calories or low-volume/high-calorie stuff.
