There is, as almost always, a time/money tradeoff. If you buy a new cargo bike, you'll like it, and it will serve you well. But if you wait and develop expertise, you'll save money.
I've been hauling kids and cargo on bike for many years. I've used regular bikes, not specialty bikes. My preferred method of hauling is with a kiddie trailer, though specialized trailers and bikes have their advantages. I can haul over 100 pounds of stuff or kids in one of these trailers. Since the weight isn't on the bike, it doesn't affect bike handling, which makes things easier. But trailers do cause more wind drag than cargo on a bike. I've gotten good trailers on craigslist for as little as $60.
If you want a serious cargo bike, take a look at the Yuba Mundo. It's expensive and heavy, but it can do everything.
Also, think ahead a few years. If you don't expect to be hauling the same kind of stuff for many years, it may not be a good investment. Unfortunately, after my kids outgrew the trailer, I gave it away. Soon after that, I realized I wanted to go shopping with a trailer, so I had to buy another one.
Here's my bike with the trailer just after coming home with a full week's groceries. I've even gone to Costco with it and hauled home a normal Costco-size load. It's really surprisingly easy to haul heavy stuff this way. And since people think there's a kid in there (and I won't disavow them of this belief), they drive around me cautiously and politely. This is in New Jersey, where people are known, deservedly, for bad driving.
You can acquire mechanical skills for bikes at bikeforums.net. I'm there often, giving out advice. We walk people through even the most complicated procedures, and they end up succeeding most of the time.