DrCosyTiger, had to answer this. Sorry to hear you are going through this - I had a very similar experience with my DD (who was 4 months old at the time) last year and I remember it well.
DD was very upset for the first 24 hours too - I remember standing out in the garden with her in the middle of the night while she cried and cried. The good news is that she did get used to it in about 2-3 days, and was absolutely fine for the rest of the time she had it on (14 weeks). I honestly don't even think she knew it was on after the first week.
In terms of clothes I mostly used larger sizes which fitted over the harness. I didn't get a special chair, as she was never a fan of the bouncy chair and was not yet on solid food.
Washing: the occupation therapist told me that I could undo the velcro straps one at a time once a day and wash her. I just used warm water and cotton wool. She did get a bit sore at times, but nothing too grim. I found Kamillosan excellent for using behind her knees and in the nappy area.
I was very upset at first, but it is amazing how you get used to it, and by the end it seemed totally normal. DD's hips are much better now - she still needs to be scanned every year until she is five, but fingers crossed she will not need further treatment. Apparently the Pavlik Harness works in 9 out of 10 cases.
Hope this helps - do ask if you have any questions.