This may seem obvious to all of you who are more advanced, but it was a bit a revelation to me:
In order to start an idle, you need to lean backwards as you come to a stop.
I did not understand his seemingly obvious (in hindsight) bit of information until tonight. I have been trying to learn idling by first idling next to a wall. I then have been trying to progress to stopping into a single idle back and then carrying on, as recommended by many in this forum. I just couldn’t do anything but come to a stop and stall or UPD. Then, tonight, I was practicing dismounting with the seat in front. Suddenly, I found myself peddling backward, just like I want to be doing in the idle. 
I didn’t progress to a full idle tonight, but I now have a clearer idea what I need to do.
On a further note, I am finally making turns at sidewalk corners without dismounting.
Also, I am starting to work on hopping (not so good yet).