J.,
Hello. Sounds like you're half way there. Here's what I did with my daughter: I let her pick her underwear out at the store and our motto is to keep them "clean and dry", we say this every time we put our underwear on, I tell her she did a good job keeping them "clean and dry" when we go to use the potty (if they are), and remind her again when we pull them up after she uses the potty. Find about 3 days when you can just stay at home or in your neighborhood. I would take her to the potty - to just try every hour and then explain that she won't have to go so often if she starts to tell you when he has to go pee or poop. I would still be aware of the time; children do get busy playing and don't want to stop. So, if it's been over 2 hours, I'd just say it's time to try to pee or poop.
Accidents will happen, and I never made a big deal out of it; however, it was my daughter that had to clean it up - meaning, she had to take her own shorts and underwear off, wipe herself clean and if it got on anything else like the floor, I gave her a wet cloth to clean it up (of course sometimes I would still need to go over it more), and then she had to carry her wet clothes to the washing machine, come back wash her hands and get re-dressed. I would ask, "Where do we put our pee and poop?" She would say, "In Potty" and I said "That's right, let's do that next time." I have always been kind and understanding (even when I just asked if she needed to go potty), and just talked her through each step of clean up. It's just natural consequences. After about two days of having to fully clean up after herself, I think she'll start using the potty even with wearning underwear.
Hope this helps. Best of luck to you.
~ J.