I have to agree with vq that accidents could become an issue, however kindly and patiently you deal with them. You have to decide on a week, or a fortnight even, where you don't go any further than walking round the block, using your own loo or potty. And that goes for any age. It's a pita but I am watching lots of DD1's contemporaries being dually trained by nursery and at home and it is taking them weeks and months. And they are 3.
Life has to be put on hold while training a child to use the loo, and more so the younger they are. The most common advice on MN is once you start there are just no more waking time nappies, which is impractical when you have long car journeys etc.
As you know I intend on starting training LO in July when we will have two weeks at home. I am even trying to organise summer nursery cover for DD1 so that I have some one on one time with LO to make a proper attempt. Because during those two weeks the outside world, apart from the odd occasion, will stop existing.
This is hard for people who work full time, and to them I would say use some annual leave and tag it on to a long weekend and do nothing else.
It sounds like I am shouting and criticising and I really am not. But going out for beach trips and to music class, however familiar to him will, IME, distract him from your current goal.
He seems ready from what you say so make the most of it, but everything else needs to stop, otherwise this could drag on for a long time. And the longer it does the harder it will be for both of you.
Again, this is advice based on my experience and observation and from the advice given to me by far more experienced people when I was training dd1. I'm not saying the way I train is right, or perfect, but in my case it worked.