I can tell you this - I have no memories from the first four months after the birth of my first child. It's just one big blur. Good thing we made lots of photos. The need to feed baby every 3 hours is going to have the profoundest effect on your lifestyle. A bit of the downtime is in fact going to be a bit, and not when you want it, but whenever you can. The regular exercise - I wouldn't be counting on it, not in first 4 months.

In short, the only thing you can be sure of is that "your life, as you know it, is gone. Never to return."