Well congrats on your biking achievements! That's something to be proud of!
You are doing a good job by walking and running and easing into the speed and miles.
Just make sure that you have running shoes made for your stride and strike. Running in good shoes is very important as it prevents injuries.
Also ease into your miles. It's not like cycling where you can make huge leaps and bounds... without the threat of getting injured. The rule is that you up your miles by 10% each week.
And when you can, run outside. It's a lot more challenging than running on a treadmill.
Good luck! Oh, and from what I have seen good runners are fast on the bike!
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"