*A is definitely a great program, IMHO one of the best alliance programs. However, your "home base" and what you value really is what you need to consider, not what is the best program on paper.

If it's only 4 flights a year, you might not mind 2-stops to get to China depending on how well your kids travel. That gives you lots of options. Direct flights are still quite limited and many of the additional direct services recently approved have been delayed by the carriers.

You also want to consider the fare class you will usually pay for. If you're likely to fly coach for paid fares, look for carriers that have premium economy (coach plus, economy deluxe, etc...) cabins. Makes a world of difference having a few extra inches of pitch when flying TPAC. For example UA coach is almost unbearable on that long TPAC segment while E+ is actually quite comfortable (at least for your legs). I know NH has E+ also, not sure about others. Highly recommend you dig into that.

If you're thinking of free upgrades to biz or first class, AFAIK, that doesn't happen as a matter of procedure. You may get ops up if you're top tier elite in an oversold situation (fare basis counts also). Some carriers give their top elites SWUs after a certain number of miles flown (e.g. NW at 100K). Apart from that, I don't know of any carrier that provides free C/F upgrades as part of the program. A few offer that for domestic flights (US, NW, CO, DL, ...) but not international.

Your last question is known as a challenge or fastrack. First thing to do is pick the carrier that you want. Call them up and let them know you'll be doing a lot of flying and ask what they can do to fasttrack you to a higher tier membership. Most carriers offer some level of matching and challenge option if you're already elite with another program. It might be a little harder if you have absolutely no elite membership with other FF programs but it's worth trying. Just remember that status matches and challenges are generally a 1-time thing so don't use it unless you know you will make it.