I have these types of existential crises about once every two years. Sometimes I just feel incredibly uninspired, which then leads to restlessness. It sounds like this might be what you're feeling, too?
That loneliness you described is more like "emptiness," and you should keep looking for inspiration to fill that space. You can find inspiration anywhere – there's no wrong answer! Woodworking, pottery, and taking classes all sound bomb.com. Some other suggestions:
You can travel. Going somewhere I've never been before, where I don't even speak the language, has reliably kicked me out of these lulls.
You can find something else to pour yourself into. In the past, I've just taken advantage of these uninspired periods by devoting a few weeks or months to another "bucket list" goal of mine (i.e. training for and completing an Ironman).
You can make new friends or visit old ones. Visiting old friends who knew me really well in a previous chapter of my life is a great way to shake me out of a funk. It's a good reminder of where I've been and gives me perspective on where I want to go. I also love reconnecting w/ people I really respect and admire, people who have also been my biggest supporters. As Rumi said, "Set your life on fire. Seek those who fan your flames."
What you've described sounds extremely familiar to me. If it really is the same thing, I'd tell you that it's normal and definitely not forever. While some people wait for something to happen to them, I'd say be proactive and go search for that new inspiration!
Ps. I'm 30 and plan to start a family soon(ish), too. Our thinking is that these are the last kid-free months we'll ever have again, so we're trying to squeeze in as many adventures as we possibly can. Perhaps you and your wife should, too!
Good luck, and congratulations on reaching this level of success w/ your business! Feeling uninspired at this point just means that you've conquered one challenge and are hungry for something new to sink your teeth into.