Your eating strategy sounds almost exactly like mine: a couple of hundred calories per hour (roughly 200 or 250, give or take, not measured precisely), usually (but not always) eaten gradually through the hour. Some people find it difficult to eat while riding, but for those of us who don't mind, it's probably a pretty good nutritional strategy. Most cyclists who are in shape and have been eating meals regularly can jump on the bike and ride spiritedly for something like three to maybe five hours (I'm about three and a half!) before they spend their body's carbohydrate reserves and their capacity to put out their regular power suddenly plummets. So, already at the "short"(!) distance of 200k, most riders have a plan for eating through the ride.
Generally speaking, 200-250calories/hour is about the maximum rate that a body can metabolize food, so if you consume at a faster rate, you'll probably just be getting stuffed with a backlog to digest, with no performance gains.
And yes -- you could say that "riding hard sometimes" is indeed about getting the heartrate up. Long story short: flat terrain & hills can each play a distinct role in training, but you know those hills that are difficult to climb? I'm sorry to say, but they're difficult to climb because you're typically forced to work hard, which is why hills are a GREAT for getting the heartrate up! The goal is not to go fast, or to keep up with anyone or to beat anyone up the hill, but to spend time where you're working hard and breathing hard enough that it's difficult to speak full sentences between breaths! It's about what you're having your body do on the inside, rather than where you're going or how fast you're going, etc. :)
On this perceived effort scale for cycling training, this "riding hard, sometimes" is 6 or 7:
Many of us will be riding brevet events spending as much time as possible in 2 or 3, but, in order to be able ride in that comfortable place (2-3) on event day and still make pretty a pretty good rate of progress on the road, we do spend some time in between events (some of us call it "training!") putting our bodies through some time at 6 or 7, and most of us do that on the hills. Another way to describe 6-7 is the range of effort that you can do for about twenty to sixty minutes -- so, people can manage perhaps sixty minutes at level 6, or twenty minutes at level 7; after that, they'll be totally fried & burnt out. In training, since the goal is not to get fried but to improve fitness, maybe spend periods of five to ten minutes in this effort level several times on a short ride after warming up.
Training at the efforts labeled as 4 & 5 has value, too -- as my training ramps up, I will work up to doing a set of three efforts at twenty minutes each, with a five minute recovery in between, for a sum total of about an hour at that effort level on a training ride. It is an effort that I can feel in my legs afterwards, but I do not feel beat up. I may do that tomorrow, actually, on a hill that takes me about twenty minutes to climb! :)
If you want to have more fun and less "homework" then you can simply go out on a ride with good friends and attack some of the short hills (five- or ten-minute climbs) at a measured effort that you can just sustain for the duration of that climb. Impress your friends with your effort! :)
Also: don't take my word for it. Talk to more people, maybe do some reading, and pay attention to your body, and maybe even get professional advice -- I am not a doctor, nor a professional trainer, nor anything like that; I'm just some guy on the Internet.
See you at the Uvas 200k?