Potty Timelines - what should I expect?

I fully realize that this is a very loaded question but I really need to know what the norm is so that I can nudge AS in the right direction...you know. AS will be 5 in the fall and misses the cut off for kindergarten (yay) so he is in preschool now. He came home from an orphanage in Eastern Europe about 10 months ago. In the orphanage all the kids sat on pots (literally) and sitting on a toilet was a new thing for AS when we got home. We currently use a stool and potty insert for him to pee and poop. He can set it up, pull down his pants and underwear, sit on the potty, do his business and pull up his pants or ask for help wiping. He also enjoys flushing and washing hands - a lot. AS also wears a diaper to sleep, both at night and for naps and they are wet almost every time. DH thinks he should be peeing standing up and my FIL thinks that he should be out of diapers completely. I am figuring that when he wants to go potty like his friends at school do, he will try and I will help him. I don't want to push too many changes in one year. What do you all think? Should I let him be or push him a little. When DH tries to get him to pee standing on his stool he bends his knees, misses and cries the whole time.