I have the problem that it's kinda hard to calculate the calories since I'm not cooking :S So I just try to eat as much as possible(of what is healthy). Is that a good way to go?
So it is ok to like... run 30 min on a treadmill?
I hesitate to say definitively that this or that is good or bad because there are so many variables and what works for you might not work for me, and so on, etc. I'll just tell you what I'd do.
I'd have to find a way to track my calories. If I don't cook, but can (have the means), I'd start. I don't cook all day every day, but I prepare all my own food (95% of the time). I usually devote some time on Sundays to preparing as much food for the work week as I can. I cook 3 chicken breasts, 7 sweet potatoes, 3 fish fillets, and some sides and tupperware those items up into some quick on-the-go meals for my lunches Mon - Fri. I also organize my snacks like almonds, apples, baby carrots, protein bars, etc. and have them sitting ready for the week. That's how I keep up with it.
If I had no choice but to grab food on the go, I'd pick 'on the go' food that I can calculate calories for. Like, beef jerky, for example. The nutrition facts are on the package. Many restaurants publish nutrition facts about their menu items. Gather the info and plan your 'to go' food intake according to your caloric goals/needs.
Running 30 min on treadmill. I wouldn't do it. If I felt I had to, I'd make sure to keep my heartrate at or below 120bpm - keep the intensity low. I have 120bpm as a target because of my age and resting heartrate - yours might be higher or lower. And I'd probably only do 30 minutes total (30 minutes including warm up and cool down - 2 - 5 minutes each).
But that's just me. You might be totally different. I've learned a little what works for me through trial and error (many many errors). I know what makes me grow, thanks to HST - and that includes tracking my nutrition daily, eating above maintainance, utilizing progressive load, hitting each muscle every 48 hours or so, and resting my muscles as much as I can in between sessions.