Experience suggests that firstly assess own condition, not just weight but all medical factors that, like a car engine, can gauge capacity. Then at a level apt for your physical state start running small distances on grassy hills for say 400m to one mile. Record how you feel and time taken. Initially every 3rd day will give your body time to adjust / recover as the most important thing for you now is to start a regime that is sustainable. Pointless gunning it early and getting tired/injured and give up. Think a year to graduate from 400m to 3 miles or further running around a park. Incorporate other easy body exercise with light weights.
We are competitive so try to make sure the first 25% of the run is a canter, do not get carried away with the hype at the start, else you will suffer dearly for half the race,run, event and aim to find a steady state, ie revs where you are very comfortable at a certain pace and never up the pace....have the same revs for the duration. If you run up a hill do not try harder, but keep same revs and slow down with smaller steps.
By keeping a diary after a year you will have a very good overview of where you are at different levels of fitness and know your body and how much it can handle without tendons et al getting sore/strained. A fit fat person is healthier than a sedentary fat person. The body was created to adjust to the demands we put on it so work with the body and not crunch impatiently through the gears for ego sake. The principal aim is to be active for ever more, even into your 80's....a way of life.
You can assist this with impromptu exercise by walking to the shops, cafe, work social sporting venues etc in addition to fitness sessions.
A way of life and do not be affected by small weight variations, as in society, it is what you are and what you do above what you look like or a measurement.
I am 96k and 6ft and 68 and run 5k weekly at "Park Run". Look up this world wide organisation jogging events held in most areas.
By running at 25% of my inate ability I am always comfortable in the run and never ever sprint...why bother to save a second if that sudden burst damages something. I often have minor niggles and recover within a day and train 2 or 3 times a week at honest plod pace where I am huffing and puffing for 10 to 20 and build up to 30 minutes around a hilly park. I know my engine can run xyz for 5k but my wheels will fall off if I tried, my young race days are over, it is now a more asthetic exercise in a challenge to keep sound such a burdened Lancaster Bomber going to get back across the channel each time I run.
Good luck and listen to your body....