It is much better if you eat a lot and do weight lifting targeting big muscle groups such as chest, back and legs.

About food, better to eat a good portion but repeat that same portion on every meal. Breakfast, lunch, tea break, dinner, supper. Add protein shake into your diet as well.

Increase muscle mass is much better than eating a lot and gain fat and bad cholesterol.

You can gain or lose fat and muscle. But you can't convert fat to muscle.

Healthier to focus on gaining muscle instead fat. And yeah, try consistently eat a lot of meals per day.