Is a garmin more accurate than a phone then? Sorry if that's a stupid newbie question, but they're all using the same satellites surely? I am tempted to get one, but thinking of leaving it till Christmas pressie time (mainly so I can get the hubby one, whereas if I get one now, he'll get himself one now!).
Our parkrun is 4 loops, 2 big and 2 small, but all clockwise, so the "keep to the left" mantra does mean slower runners (like myself!) will run farther than the faster runners. I don't expect there's 300m in it though, which is what mine and hubby's phones fairly consistent measure the course as (5.3km).
Don't rely on running to lose weight. It can help, but diet is the main part. Losing weight will make running easier.
As as others have said, start slowly. Try a couch to 5k app, but don't feel you have to progress as quickly as it suggests - some go over 6 or 8 weeks. I did one that was over 10 weeks, but I repeated multiple weeks so that it took much longer. When I originally did this, it was 3 years ago and then I got out of the habit for 2 years and have only recently taken up running again. 3 years ago I was running, but not paying much attention to my diet, so I wasn't losing weight. This year I've lost 1.5 stone and I am getting better times already than I was after much longer running 3 years ago.
The only way I can run in the evening is to do it straight after work and before I get home. I take running gear to work and change before I leave, drive to where the kids are in after school club, run, then collect the kids. If I go home, or in particular if I sit down on the sofa, then all is lost. I also run in the evening when the kids are in a karate class. I have to be there anyway and it's pretty dull sitting watching. It's an hour long, so that gives me time for a run followed by a shower in the sports centre where karate is happening.
It's the margin of error on the device that I'm thinking of though. I'm trying to run 3 times a week, one of which is Parkrun. The other 2 runs I run 5k as measured by my phone and I believe it but then do I compare that time with what my phone measures as 5k of the Parkrun or do I compare it to the whole Parkrun. I know, it doesn't really matter...