1) Less and more than you think. Bank on at least one to two hours out of every four (that's about their sleep-wake cycle for the first couple months). Very little of it is hard if they're not sick, but the cycle is relentless.
2) Babies are very portable for the first 6 months or so b/c they're so oblivious to the world. Wake-up, change them, feed them, interact for a while, put them back to sleep for another 2 hours and they don't care what else you're doing. One parent having a full time job is easy, two is expensive and hard. Downtime is plentiful because of the frequent naps. Ditto for exercise as long as you're going one at a time while the other tends baby and unwinds.
Ironically, scheduling is much harder once the baby sleeps through the night, because at that age they're much more alert and aware during the day and therefore need a more rigid nap time routine. It gets a little better around 12-18 months when they go from two naps to one, and even better around 3-4 yrs when they drop the daytime nap and stay up all day.
Your math about sleep cycles is way wrong, and the idea that you'll still have half the free time you used to is laughable. Assuming a more or less 'normal' work schedule, most of the time they're sleeping, this guy will either be at work or will be sleeping himself.
My advice is to assume that for a few years you're going to have very little downtime unless you don't sleep much or don't feel the need to see your wife much.
P.S. never let them outnumber you
I'm a middle child, and yes I suffer from middle-child syndrome big-time, still. Working class background, mum was a housewife and dad worked in a textile mill. Its amazing how he managed to raise us on that salary, yet 7 out of 10 of us have at least a degree, going all the way up to at least one PhD.
In short, the only thing you can be sure of is that "your life, as you know it, is gone. Never to return."
Pretty much the rest of the developed world gets 1 year parental/maternal benefits as a social construct.
Of course, a new born obviously requires a lot of attention (I have a 3 month old), but let them breath as they get older.
My point was that as a father of two boys, I can tell you that as far as priorities go, they are by far number 1, and they occupy pretty much all of my free time, either directly or indirectly. Of course I do make time for other things like work and my wife and trying to get a startup out the door.
Or to put it another way, here's the Springfield Nuclear Power Plant softball team: "No one can give more than one hundred percent. By definition that is the most anyone can give..."
In time you'll get some of your life back, but it can take a while depending on the baby. It's worth it though as you'll be amazed by how much you come to love the little pup.