Potty Training Update

I'm really clueless when in comes to successful potty training techniques but we're giving it a shot. Last week we bought a potty chair for Warner, hoping it would catch his interest. Up to that point, we were using a seat on the big potty and he had never put anything in the potty when he tried. The potty chair was $12 and he was excited about it at the store (it is a frog, after all) so I thought it was worth a shot.
When we got home he pottied on it immediately. I was so excited I almost cried. We made a big deal of it, calling Bobbie and Grandpa and Nanny and Grandaddy to tell them about it. Warner was so proud. He went to Maren to tell her: "Mono - potty, me!". I didn't have any small candy to give him as a reward, but, seeing as it was the first time he ever peed in the potty, I thought a big reward was appropriate. So, we gave him a piece of Dove chocolate.

The next day he woke up and wanted to pee in his potty. He was successful on his first try, and quickly remembered the Dove chocolate from the night before. I gave him a piece (it was 7:30am). He insisted on staying naked, and I agreed, thinking it would be easier to manage the whole process. Here he is eating a snack, in the nude:
(I realize visitors are probably never going to want to sit on that couch again. Don't worry, he didn't have any accidents on the sofa). He had two accidents (and I think ate 8 pieces of chocolate) that day, but overall, I considered it a successful day. He only had 3 pairs of big boy underwear, so the following day we went to Target to choose new underwear as well as smaller candy for rewards. He chose Elmo and Thomas underwear and Reese's Pieces and jellybeans for candy. This shot was taken after a successful trip to the potty chair, in Sesame Street underwear, and with the chocolate reward, of course:Since then, it's pretty much been downhill. He went nearly two full days wearing a diaper, completely not interested in wearing underwear at all. He has pooped three times in his underwear, despite me promising HUGE rewards if he poops in the potty, and being very sad when he poops in Elmo or Thomas.

I'm not sure how to proceed from here. I'm sure it's confusing for him when I put a diaper on him at naptime, bedtime, and when we go out. And, I'm pretty confident he only pees in the potty to get the candy. Not because he necessarily wants to, or even understands when he needs to. The kid will eek out three drops, then proudly tell me he peed and ask for his candy reward. So, we'll see how this continues. It would be so nice to only have one child in diapers, but until then I suppose I'll just have to be patient.