There was a barrier around the W3 mark. I experienced a lot of chafing on my arches. Wearing two pairs of socks and a strip of Strappal tape on the chafed spots worked.
I started skipping rest days and doing more runs because I felt OK, better than OK. And also for 2 other reasons - 1. I felt that doing more runs together and taking a single but slightly longer rest period was more beneficial, and 2. I wanted to avoid inertia pains that came with taking too many rest days/periods. I would do 2 or 3 days of consecutive running, followed by 2 or 3 days of not running (I went swimming instead).
From W4, I started extending the runs. I would run for another song's duration. This followed with a 3-song extension - run for 1 song, walk for 2nd song and run for 3rd song. I had seen W5R3 and I guess this was my own way of making sure I got through that.
From W5 on, I extended my run so much that the entire C25K session would account for the outward part. This effectively doubled the exercise/distance. I would run, run/walk back. On W5R2, I did the session (8 min run, 5 min walk, 8 min run) and after the 5 min cooldown walk, I ran all the way back.
W6 on, I was simply doubling most of the sessions. I finished W9R2 yesterday, and I'm due a few rest days. Later in the week, I'll do the last session and start on a 10K program.
These are some of my other thoughts following my experience so far.
Drinking a lot of water on run days. I also eat a fair bit.
A great pair of running shoes helped a lot.
A great playlist is a must. They are songs I love. (High energy, high-BPM music only got me disinterested.) Sometimes, the right song comes on at the just the right time, and it gives me just what I need to push on.
Posture is critical. I did a bit of research here. My run-posture mantra is feet forward, back straight, relaxed hands, keep head level as much as possible (not bobbing), un-tensed feet.
I went at a pace that was almost always comfortable to me. Sometimes I would even sing along to my playlist (I run v.late at night or v.early in the morning usually). Math-wise, 30 mins for a 5k means 10 km/h. I ignore that. Speed will come with practice later. I pushed myself through a run in W8 at a faster pace but only resulted in giving myself nausea at the end of it.
Listening to my body. This is by far the most important thing. In the past 6 weeks or so, I've started to understand some of the things my body is telling me. I believe that in a limited way, I can now tell the difference between a pain that's happening because I'm pushing a new limit and it's just the muscles complaining, and a pain that needs me to stop. There are many other types of messages (and pains) and I'm still working on wrapping my head around this.
Finally, I have to say that I love this app. Before this, I have never been able to run for any significant distance. It has, very literally, taken me from the couch and has enabled me to run. And it has somehow also have fun while doing it.