Just Learning
Congrats on your surgery and welcome! At 1-2 week post op my doctor told me that fluids (64 ounces a day) were the most important thing to focus on and to get in some protein when I could, usually in the form of protein shakes, which I started on day 3 (2 a day, 30g of protein each). I also ate ~1-2 Tablespoons of broth, strained cream soup or yogurt 3 times a day at that point.
Really at this point you have only two goals per day. Getting in a minimum of 64 oz water (flavored or otherwise) and I was told 80g protein as a goal to shoot for. However follow your surgeon's plan and you will do great. Eventually you will get to a point where you will be shooting for about 600 to 800 calories per day and 40g carbs or less per day while getting in the above proteins and water.
So your number one goal isn't calories as much as it is the liquids and proteins ... calories will fall into place as they should.