B. - If he is consistently taking off his diaper when he is dirty, then I would start with that. Not all kids wait until the time the "experts" say they are ready. Some are even later. He may really be thrilled to be able to flush his own TP down the toilet. Start catching him in the act and rush him to the potty.....He will soon realize what you are doing and my even rush himself to the potty.
Also, if he is really that uncomfortable being wet/dirty, then he will be even more so in underwear. What works for one child doesn't necessarily work for another. But, always give a system a fair trial before deciding it won't work. My son liked to "aim" at the cheerio in the potty, then he was rewarded with coins (he was into money at a very young age). My first daughter liked to get an M&M after she had a good potty experience. My second daughter is motivated by "helping Mommmy". The last one doesn't seem to want to tell me when she has to go, but as long as I take her to the potty every few hours, she stays dry and clean. And if I forget for 4 or 5 hours she holds it. It works for me, for now.
He will learn quickly what it feels like to need to go pee if you put him in underwear. Diapers seem to keep them too dry for too long.
I liked the eBook I found on www.thepottytrainer.com. You might want to check it out, as well as, other resources.
The thing that worked for all of mine, is to tell them they are not a baby anymore and this is how it is. Good luck and think of all the money you will be saving!!!
A.
Working from home with 3 Blessings.