I had problems with this and took my shoes back to the running shop, they applied a blister patch to the shoe in the area that was rubbing over the joint between the inner sole and the shoe. This worked a treat, might be worth a try. Other people have spoken of different ways of lacing their shoes as well.
Mobile phones and the tracking apps are not known for being the most accurate. I have tracked a walk and compared it with someone else using the same phone on the same walk and come up with different distances. What you can assume though is that if you consistently use the same device the same margin of error is applied to all of your activities therefore in my opinion you do not need to worry about it.
Parkrun may not be as accurately measured as certified races but it is free and available to everyone and is doing a great job.
Well done for getting started, that is really quite tough! There is the possibility that you are going too fast, this is common when starting out and the guide of being able to hold a conversation is a good one. I also like the idea of repeating some of the earlier weeks, it may just be that your body needs a little longer to get used to the idea of running. By doing exercise while also looking at your diet the weight will come off slowly and steadily, trust me this is the best approach! As for blood pressure reduce salt intake and caffeinie too, drink water and the exercise should help. Running outside is much more fun than the gym, do you have some local friends who could walk round some proposed routes with you? Walking may help too as it is time spent on your feet.
My first R4L I took about 55mins to cover the 5km and wasn't last. Many people walk it and for many people taking part the challenge is completing 5km under their own steam let alone running it all. It is a really relaxed celebratory atmosphere so I suggest you go ahead and do it and most importantly enjoy it!
Then you can come on here and tell us all how well you did and what you are going to do next...