Heya,
It sounds like you're taking a really sensible approach to this with some good, achievable goals. I think you're right in that a lot of people do gain weight at university for a combination of reasons.
Sometimes working from a basic 'meal plan' can help - it might be useful to plan your meals for the week in advance so that you buy in what you need and can prepare it in advance if necessary if you know you're going to be busy. When you cook yourself your homemade meals, can you cook in bulk and freeze some portions so that you've got good healthy meals just ready to be heated up when you need them?
Same with lunches - if you can prepare them in advance (e.g. the night before) it can save time in the morning and stop you from buying unhealthy convenience food. It's ok to snack, and like you say, it's far better than going out a drastic diet, trying to cut everything out and then regaining the weight! But it's worth thinking about and buying in some healthy snacks so that you have those to hand too - things like nuts and seeds, fruit, flapjack bars and Nakd bars are some of my favourite things personally.
When I was inpatient and saw a dietitian, one of the big things we focused on in Nutrition groups was the 'third/third/third' idea for meals - so having meals based on a third protein/fat portion, a third carbohydrate and a third fruits/vegetables. If you're already cooking homemade meals this might not be very useful, but it's a good basic guideline for healthy, balanced meals otherwise.
The other thing to think about if you're wanting a healthy lifestyle is exercise - are you getting regular exercise at the moment?