2 pieces of advice, one financial, one not.
Financial: this is a great time to investigate your assumptions and expectations about what you want your life with kids to be. The reality is that kids can cost very little or a metric shit-ton; the difference is all in what you mean when you say you want to "plan" for kids. Does that mean daycare, 2 full-time jobs, car at 16, fully-funded college, etc.? Or everyone retires to a small farm and lives on what you can grow yourself? Most folks are somewhere in-between. But every option has financial ramifications, both on income and expenditures, and so you want to ensure that your financial plan meshes with what you want to provide for your kids. What tends to breed unhappiness is when what you are doing varies from what you think you should do -- e.g., if all the other kids in the area have/do X, and your kid doesn't, that can breed guilt. So you need to have a very clear vision of what you do and don't want to provide, and find your tribe of similarly-minded people, before you find yourself in the middle of the muddle and aren't understanding why life seems like a never-ending treadmill of stress and meh.
Also, then you should prepare to be entirely wrong and to revisit that plan routinely. ;-)
Non-financial: Remember that it is your job to adjust to what your kid needs, and not your kid's job to adjust to you. Kids and parents come in all different collections of temperaments and abilities and weaknesses, and not all of those naturally fit together well. But raising emotionally healthy kids requires that kind of meshing; the kid needs to feel loved and secure and know what the limits are, and you need the kid to behave reasonably before you start tearing your hair out. But the thing is, between the two of you, which one of you has the maturity to make that adjustment? Kids don't have the self-awareness to realize that what they're doing isn't working; you do. I mean, a baby is going to cry when it's upset rather than think, "hmmm, my crying really annoys my dad, so maybe I should learn to speak so I can communicate my wants." You, OTOH, can realize that you can "parent" in many, many ways, and you can see each approach as a different strategy, and you can therefore elect to change your strategy when what comes naturally doesn't work for your kid.
I speak from very personal experience with the hellion known as my daughter. She was very ADHD, very extroverted, full of energy and life, super-sensitive to things like tags on shirt, and a giant rolling bundle of need for constant attention and reasurance and love; she's got the crusty outside and the gooey middle. I'm an introvert who needs lots of downtime. She freaking exhausted me, and absolutely none of the parenting strategies I learned growing up worked ("ignore a tantrum"? HAH!). I worked my ass off for the first c. 4 years of her life to figure out what would work ("1-2-3 Magic" and "Your Spirited Child" saved both our lives).
My DH, OTOH, has a very authoritarian parenting style and pretty much expected her to adjust to him. He'd read the books if I made him, and he'd go along with various disciplinary approaches, but he never really got it. His authoritarian approach would just amp her up and make things worse until she'd go into a total death spiral. So I ended up basically parenting him along with our kids, which wasn't remotely good for either our marriage or my stress level (and 20 years later, DD still prefers to talk to him through me). In short: don't be him. It is your job to communicate effectively with your kids, to establish rules and limits that are clear and consistent, and to always make them feel secure and loved. So when what you're doing isn't working, it's on you to try something else.
And then once you've figured out what works with your first kid, assume that your second kid will be entirely different and you'll need to start over from scratch. ;-)
