becky, a couple thoughts. first 21 months is a little young in my opinion. my son has no communication issues, and he was three. so don't sweat it, he's not a freak or anything :) S., the peeing standing up, don't even worry about it. my son started doing it all by himself (all i heard was, hey mom look what i can do! and i was shocked lol) once he started preschool. he'll pick it up.
last, if you want to introduce him, great. just don't push it. this may be a year long process. if you get frustrated it will discourage him from wanting to. be positive and encouraging and let him be your guide. either he is ready, or he isn't, and nothing you can do will change that fact. when he's ready he'll do it willingly and it will be a breeze. good luck!
(PS one more thing - my son never used a potty chair or a ring - we had a potty chair but he was never interested. he wanted to sit on the big potty like everyone else. potty chairs and rings can be nice for little ones, but they aren't necessary)