I agree with all above, . I live 3.1 miles from work and i run one way then cycle the other.
importaint to listen to your body, i have quite a manual job so i sometimes have a rest day wednesday. either cycle both ways or drive.
you can build it up. i was running both ways 4 days a week then cycling wednesday in Aug. after months of bulding up to it. also depends how fast you are running it. if you are slow jogging or running, depends on if you want to build up to speed or endurnace ie get faster running the distance or making all 35 miles.
one more piece of advice is diet, when i started doing this about year ago, i didnt eat enough and my legs were heavy running home and the next day. So make sure your body is fuelled up for it.
can I just say it took me ages to decide to whether to get one...in the end i did and i never look back. i dont know if it is possible, but if you go to garmin connect and look at peoples runs, you will see it really does follow footpaths and such. it is as accurate as something that size can be. i do recommend locking the bezel once underway as mine did play up once underway as it was raining, but normally i do and never have any problems. i dont use a hrm but i use the speed and pace setting and find them useful when training.
one piece of kit, although really highly priced, is great is a gore windproof top (it is water proof, and breathable) it is about £80. I have one and never needed anyhting else. It keep me warm in the winter without having to wear a jacket and it manages to keep me cool, once running. it looks thin and like it wouldnt be enough, but without sounding like a gore salesman it really is all you need. it has the hand cover on the sleeve as well, leaving fingers exposed, but hands stay warm,
As a driver and runner and cyclist I have always used static lights not flashing. I think it is a bit distracting, yet a static light does the job and doesnt cry out "look at me".
I carry a backpack when running to work and even though i am on the footpath i use a light on my back. more for cyclists than anyone else......though i feel they should be on the road really.
I must admit though cyclists are worse than drivers when i am running, especialy on footpaths (i learn and TRY not to be a pain to runners when im cycling...honest). One even hit me once and cycled off. i sprained my ankle and couldnt run for a week. i even had the humiliating walk home...i was still over a mile from home!