We had a stepstool that the children could decorate with a sticker every time they went potty. They seemed to like it better than a chart, and it ended the mysterious sticker deposits elsewhere in the house.
As for your son going sooner: my boy practically potty trained himself and was totally trained (even at night!) by 27 months. I really had nearly nothing to do with it, aside from the first couple of times of showing him the potty and getting excited and congratulating him when he used it. He really did all the rest.
My daughter....oy. I didn't think she would ever, ever pee in the potty. She would go in there to poop, but it took forever for her to want to pee. But one day she did, and she was all excited and it took off from there. It took her longer, though, and longer to last through the night, too.
Sounds like you've gotten good advice, and you're doing the right stuff!