There is the stipulation... I was like running 30min. burns way more then walking 30min. but if you go the same distance then I guess it would be closer

I've always heard the magical "fat burning zone" is not accurate at all, or that it doesn't apply to everyone, and that starvation mode is a myth

The fat burning zone is something of a myth. It is calculated to be the zone (heart rate) whereby most of the calories you use are drawn from fat.

It is not the zone whereby you burn the most calories. At higher rates of exercise, you burn more calories, including more fat calories.

I have read that exercising before eating is a bad thing, in that the body senses it is at risk (no food) so draws on glycogen and lean muscle mass while protecting its critical fat reserves. Better to eat say even half a banana, then exercise.

On walk Vs run over the same distance. Looking at the activity calculator here, which I find correlates accurately to the data on my rowing machine, a 4 mile walk at 4 mph burns 424 calories, while a 4 mile jog at 6 mph burns 565calories, so not the same deal at all.

On over-doing cardio: if you kept your heart rate to around 65% maximum (start with 220 - your age in years as your maximum) you would be safe to keep going longer than the OP reports. But you need a heart monitor (around ~$50).

As with most simple questions, there is no simple answer!

It really depends on the intensity of the cardio, and your goals. If you are aiming to loose weight, and do moderate intensity cardio (i.e. where you are working at 65% of your max heart rate) you can do a lot before you do 'too much'. If you are aiming to improve your cardiovascular system and workout up in the 80-85% (or higher) you can easily do too much, and 'overtrain'.

A few years ago I was in your current position. The best advice I was given....'buy a heart rate monitor'. I was able to monitor my 'real' effort - was I working hard, or just thinking I was working hard.

Life is a marathon and not a sprint!!! Remember that