Newbie to running here ^_^

Well, 1 mile = 1.6 kilometers so you ran about 3/4 of a mile in 7:43
That puts you roughly around 10+ minutes per mile or around 5MPH average (closer to 11 minutes and under 5MPH).

Too many numbers, meh

I don't know if its average or fast or mediumly average fast, but if you haven't run in a while it's a good enough pace.

Tips for improving stamina? Run more often. I tend to start off on a treadmill after a long layoff to get back to being used to running, until i get bored of it then I hit the streets. I find this ensures that I don't start running weird and can fix it before the harder impact of the concrete starts to take its toll on me.

Good luck

I would suggest that you try following a plan that encourages you to build up by walking a bit and then running a bit. I wouldn't worry too much about your pace to start with, it is tempting to want to run faster, but it is best to get a proper pace first.

don't worry about not having a HRM, just make sure that you can still talk quite naturally at the pace you are running and if you feel too out of breath to talk, you are going too fast.

See these links for useful plans

http://www.coolrunning.com/engine/2/2_3/181.shtml

http://www.bhf.org.uk/get-involved/events/training/running-training-zone/running-training-schedules.aspx