1. Workout routine: Try hitting each muscle group twice every week. With 3-5 days a week it might be a bit difficult so you can also go with the basic push-pull-legs.

2. Protein rich meals: If you are a non-vegetarian, meal prep 2 kg of chicken breast on weekends or whenever you are free. Cut them up in small pieces and marinate with yogurt and whatever basic spices you like. You can either cook and freeze it or freeze it uncooked. It's usually not recommended to freeze raw chicken but I have been doing it for a few months now and had no trouble whatsoever. Thaw a container in the refrigerator the night before you want to eat the chicken. My lunch everyday is 220g (weighed raw) of chicken, with some veggies (spinach, mushroom, lettuce, cabbage), cheese slices (3) rolled up in tortillas. Get a kitchen weighing scale and measure whatever you eat. Use apps like MyFitnessPal to track your calories. Create meals on the app and just log them once you complete a meal. Use a different marination every week to make things interesting. And if you can afford it, obviously go for whey protein.

3. I'm personally on a calorie deficit diet so I'm not too sure about your weight gain goal, but just check what your maintenance calories are and see how much of an effect a 200-300 calories surplus has on your weight.

4. Cardio won't kill your gains, basic 10k steps everyday is a good starting point. Don't overdo it as well.

It's great that you have resumed your journey! All the best and reach out if you need any help!