Thanks for all your questions. I'm going to try to answer them all as best as I can. Just know that everyone is different and no two FTMs are exactly alike or have the exact same experiences.
1. Yes, J will most likely be on T for the rest of his life unless a medical, financial, or personal reason causes him to stop. The permanent effects of T are increased facial and body hair, lowered voice, growth downstairs, and possible male pattern baldness. Changes that can be reverted back are fat distribution from a male pattern back to a female pattern, that time of the month if the organs are still intact, acne may decrease, sex drive may decrease, and lipid levels may return to pre-T levels.
2. I think by asking these questions and learning what you can about FTMs, you are making a very good effort to be sensitive. I would suggest looking up TMatesFTM on youtube. They make videos for significant others of FTMs and give tips on how to handle anything from pronouns to prosthetics. Speaking of pronouns, whatever your guy calls himself or asks you to call him, respect it and practice it. Even if he hasn't started T yet, chances are he still wants to be called he, him, etc. Ask if you aren't sure.
3. Most likely J is talking about top surgery. If he hasn't already found a therapist, he will be looking for one and then going to see them for a period of anywhere from about 3 months to a year give or take. After that time is done, the therapist will write a letter for surgery, hormones, or both. Then it's just a matter of finding the right surgeon, making an appointment, and getting the procedure done. During this time, you can support him by giving him space or listen after tough sessions or offering to go with him to appointments.
4. I'm not Asian, but I've had to bring my girlfriend home to meet my parents before so I know how that goes. Find out before you go how his parents are in regards to his transitioning. Are they supportive? What name does he go by at home? Does his family use masculine pronouns? Ask J what he feels most comfortable with as far as that goes. Otherwise, just do what you would normally do with a guy.
5. If the two of you are close, I see no problem in asking whether or not he's started T. As for what restroom he uses, you could ask, but I would try to ask it in a way that's not as outright. Maybe if you get on the topic of binders or packing, you could ask about STPs (stand-to-pee's) and say something like, "I read that some transguys use an STP to go to the bathroom. Have you bought something like that?" Or whatever you feel is most appropriate. When you're out somewhere, don't make a big deal about what bathroom he uses. If he uses the girls, then that's where he's most comfortable at the moment. If he uses the guys, ditto.
6. Unfortunately, science has not caught up with us as much as we'd like it to. Adoption would probably be your best option if artificial insemination is not attractive to you. Having children is a joint decision, though, so I would talk to J about it and see how he feels.
7. I haven't heard that straight guys don't like knowing their girlfriends are bi. If J only likes girls, then, yes, treat him like a straight male. His sexuality is separate from yours. You don't have to be straight for J to be straight.
8. If you are passive and he's more dominant, then you could let him lead. I would ask him upfront, like you said, about it though. I wouldn't try to assume or guess what another person likes just based on their personality.