Well of course the first thing in preventing running death is to see your doctor and make sure you are healty. That is especially true since you are 40. It would be useful to get an electrocardiogram as part of that visit if it is permitted.
I'm not sure what running deaths you are referring to because I live in the US, but quite often, those occur during marathons. Your running is nowhere near that. The rate of death sitting on the couch is pretty high if you are overweight and out of shape also. Do what you can to ensure that running is safe for you and then don't worry beyond that.
Heart rate. The max heart rate formula is basically rubbish. It tells you within 10 +/- for the majority of people, but for a small but significant minority, it bears no resemblance to reality. The problem is that without actually testing your max heart rate, you have no idea which group you are in. And if you actually test it, then you don't need the formula anymore. For fit people, I recommend actually testing it, but not for newbies.
The best way to determine if you are running the proper speed - nice and easy for now - is to try talking. You should be able to talk fairly easily. If you can't, then you need to slow down. As far as speed goes, don't worry about it. The first thing you need to work on is endurance. Speed comes later. If you don't have endurance, you can start fast, but you will not be able to sustain it. For newbies, always distance first, then speed.
