With limited patient history provided, I won’t recommend increasing calories further. Current intake of 1300 (~32 Kcal/kg) is considered high for this kind of patient. I don’t think weight gain is an objective for this patient. You are already observing adverse effects in terms of deranged LFTs. You also need to look at lipid profile as patient is receiving ~75% calories from lipids. Ketogenic diet for patients with cancer is new concept that’s is still under investigation. Theoretically, lack of carbohydrate supply creates oxidative stress in cancer cells and sensitize cancer cells to standard radiation and chemotherapy. Not much literature is available. I don’t know If stomach cancer is also involving the remaining gut. If remaining gut is accessible and functional, you should also look at the possibility of tube feeding (e.g., Jejunostomy Tube)
1000ml drain on daily basis is a lot and definitely need to be replaced. You need to look at fluid status and calculate/estimate fluid balance and make up the difference with extra fluids.