Here's the low-down on the jets:
You should have 72/115 main jets and a 38 slow jet (not sure if your slow jet is removable, I think it is). Keihin jets are widely available from places like jets-r-us. Do not buy an aftermarket kit that says it has the proper jets, they won't be.
Yes, that o-ring is included in the Honda gasket set, part # 16010-413-405.
Don't know about the needle.