Hello, I've looked into the whole J-1 thing and would like to share a few things...
1. J-1 Waivers - marrying an American or having a child in America does NOT qualify for the waiver, unless you can prove that it will cause extreme harm to the American citizen. The idea is that when you applied for J-1, you know you need to leave for 2 years so you should have planned on it. Your spouse/child can leave with you and unfortunately, excuses like "my spouse will lose a great job, doesn't speak my native language, etc." don't cut it. If you want to claim medical hardship, you'll have to prove that your home country can't provide quality medical care for your spouse's/child's condition. In other words, it's hard to get. Also, the "no objection" from home country waiver does not apply to physicians.
2. In order to apply for H1B, you need to pass step 3. Most states also have a requirement of having 1 to 3 years (varies from state to state) of post graduate medical training before taking step 3.
The advise I got from my school's international office is that if you intend to stay in US, it's best to avoid J-1 completely. Getting that J-1 waiver can be extremely difficult. For those who studied in US med schools, get OPT for the first year and then try for H1B or get married while on OPT (assuming you're engaged already, of course. I'm not suggesting you get married for the sake of staying in US). For those in international med schools... sorry, I'm not sure if you can get H1B right away (I'm in US so I only looked into the former).