We're 3.5 months into this now, and here's a summary of our experience. In short, how you balance financial goals and domestic happiness is almost entirely based on the temperaments of your kids.
Our firstborn was an "easy" baby: very rarely fussed, always slept a lot, started sleeping through the night early on, etc. She was also an "easy" toddler: super-sweet personality, never needed any disciplining, etc. We knew it at the time that she was easy, but didn't fully appreciate it until the second came along.
The second-born has been pretty much the opposite. The inconsolable screaming started around two weeks. We've tempered it with acid reflux meds (first Axid, now Prevacid). We're lucky in that she usually sleeps through the night, but the days can still be hard, particularly on my wife, who is a SAHM. Some days she will not sleep at all during the day. She's content if she's swaddled, held
and bounced constantly---omit any of those and the screaming starts. But this is tiring for my wife, plus it makes it that much harder to keep the toddler out of mischief.
It's clearly been hard on the toddler, as she's started acting out and throwing tantrums. It's a
huge adjustment for her. We found an at-home day care in our neighborhood (can walk there in a couple minutes) that we take her to twice a week. This was mostly for my wife, so she gets a break from being the single fireman faced with two fires. This has been a mixed blessing: on the one hand, my wife gets a bit of a break. But on the other hand, it's that much more of an adjustment for our toddler,
and she's learned new ways to misbehave from the other kids. And there's obviously a big cost to the day care.
It's much better on the weekends with both of us there. One kid always gets some attention, instead of 50% attention. But on the evenings when I get home from work, everyone is exhausted, and there's quite often a lot of crying until everyone is in bed.
My spouse is a stay-at-home-dad and I get 6 months PAID time off, but I'm considering taking even more time off (in Canada, I can take almost a year of minimally paid time off if I want), especially since I had pretty bad post-partum anxiety last time, which exacerbated the sleep deprivation.
I think it totally depends on the kids. If our second was like our first, I really think our lives would be about 1.1% harder. But the reality is I feel like our lives are 500% harder. If I could have stayed home for six months with my wife and not lost any pay, I would have done it without thinking. By six months I hope things are better. But based on what I've read about super-fussy kids, it could be a full year before our lives have some semblance of being normal.
Unless you have an easy baby, the key, if at all possible, is maintaining a 1-to-1 adult-to-child ratio. With only one parent, it's inevitable that if one kid is unhappy, the other one is as well. E.g., the baby starts crying, so she gets mom's full attention... but now the toddler is throwing a fit because she's not getting any attention.