My dd was just over age 4 when she first started using the potty. I remember feeling all of the things you are feeling now--
IdahoMom: Put him in the bathtub (not full of water, just to contain the mess), hand him the wipes, and let him clean himself. You'll have to instruct him the first few times, but he's old enough to be able. He'll figure out that the toilet is more convenient. He's in diapers because it's easy.
Also, he should clean any mess he makes in the bathroom/tub, as well. Natural consequences. . . we make a mess, we clean it up.
This idea sounds good on paper. But when I think about applying it to my 3.3 yr old, it would be extremely punitive. I did try this method with my DD when she was close to 4. She really wasn't able to do a proper job of cleaning herself up, for one thing, and this just made the whole diaper/toilet thing more emotionally charged. It sure didn't encourage her to use the toilet, just made her more upset about the whole thing. She needed me to be utterly loving, patient and understanding with her. She needed me to be OK with her not being quite ready for this huge change. When she turned 4, we began going without diapers full time. (this was her choice) She didn't use the toilet at all, just wet or soiled herself wherever she was. She didn't care. But she still needed me to be ok with that. After one month of constant cleaning and laundry, I told her we'd be going back to diapers because I didn't want to do it anymore. I said if she'd just TRY to make it to the potty when she had to go, that we'd keep doing it this way. So she did. That day she used the potty 5 times and within a week she was always using it. There were a lot of accidents. I'm pretty sure she had/has a difficulty in knowing when she has to go--she still isn't able to hold for long--when she has to go, she has to go right that second. I learned so much from this experience.
So that's my story...now for your diaper-changing issue. My DS is just over 3 and hates diaper changes too. Sometimes I let him go, waiting around until he's ready to lay still. Sometimes if DH is around he'll help by distracting/holding him while I change him. Sometimes I get very frustrated and yell. And we know that doesn't help! Is there any special toy that will keep him distracted while you do the job? We have this plastic recorder that DS can play only when he's having his diaper changed.
I find the worst behaviours go through cycles--it seems so bad and like he'll never stop doing it, and then it suddenly gets better.