Got great advice form here 10+ years ago when I started.
You are aerobically fit from cycling but your joints aren’t !! Your cardiovascular system can do more work than maybe your body can take.
I didn’t go over 5/6kish for probably 3 months and it served me very well, did a marathon pretty easily later that year.
Stop/starting is great, walk the stops …. I still do that now if Im not feeling it… just enjoy your surroundings.
Be careful …. You may end up ditching the bike !! I certainly have with the MTB. It’s just too much faff compared to throwing your trainers on and getting out the door
Good luck
Ditch the phone … if your loop is 6k you are what ? 20 min walk at most back you your house… Key under the door mat/plant pot.
Have fun