FFF,
I have nominated this for the BBC's "The Big Read"
Anyway, regarding the navigation. I was taught to do DR pretty to a similar method in my PPL as you are now. Basically, I needed to always mark down the half-way point (not quarter unless a very long leg), but this was simply to be able to quickly work-out a heading correction using my 10nm thumb as the half and quarter markers help you to make a glance estimation of how far you have travelled. The difference being that I was taught to only time to significant visual features, about every 6-10 mins as you do. My ETA updates are based on my arrival time at a visual feature with a judgement on if the ETA will continue to change (wrong wind) or it was simply being off track for a leg.
As for the not looking at the chart within 2 mins of arrival at a check-point, that is also how I was taught and still do it (more or less). I find it works pretty well, except it is pretty impossible not to think "Where am I" mid way between two check-points. My instructor was adamant that I keep looking out, rather than in. However, the lookout is something, as you mentioned, that I know I start off doing well, but will obviously require more constant practice to make instinctive.
Anyway, I will keep using this DR method in anticipation that it will be required learning for the CPL.
Cheers FFF, great reading
HWD.