Couple of things. How desperate is his need for green card? Is he on a brink of loosing his f1 status or no? How soon is the wife eligible to file citizenship? Okay now, if ur friend is in good status and if the wife qualifies to apply cotizen soon then I would wait till she becomes citizen. And don't get into false impression about people saying it takes 5-6 years of u file right now. It's when you file and how long after your application your petitioner becomes citizen. I -30 is just the beginning of the process, it don't take more than 5-6 months to process, what you should be worried about is the I 485 which is change of status application and thats what takes longer time to proceed than the I -30. I -30 simply verifies your relation with the petitioner. Things like stopping at the airport, loosing f1 status after your ur application( don't worry about these things as long as the relation itself is Bona fide). One more thing as long as your application is pending with uscis u can always travel with travel document if there is need to do so and you can always apply for work permit. Hope that helps.