Yes, never too late to make amends.

Excellent questions. I'll add my thoughts, but I suspect you will hear more from others.

Do enroll your wife and newborn also.

I'd also enroll in more than one alliance. It is free, and you never know when your circumstances might change and you find yourself flying a different pattern.

I'm going to give a "Sky Team" example since my nearest airport is MSP (Minneapolis-St Paul) Minnesota. Sky Team's Delta pretty much owns the situation here. So - I belong to Delta's program. If I happen to find myself on Malev, Alaska, or some other members of the Sky Team alliance, I just give them my Delta Frequent Flyer number. Then all my miles accumulate in one place.

After you've gotten yourself signed up, do read the fine print of the alliances. It can be a little tricky. An example is when Continental used to be part of Sky Team. I could indeed get miles on them for my Delta account, but ONLY 50% of the miles flown. And sometimes the less expensive fare classes don't qualify.

Then start following the chatter here as you have time (not much with a newborn, but ....). There are lots of other ways to accumulate miles - credit cards is a major one. The web sites of the airlines can have little deals like signing up for email that are good for a quick 500 miles.

Romelle