There are excellent 3D wood design software options on the market, but I'm not going to mention them, because I prefer free software for designing furniture. I use SketchUp and love it. It used to be called Google SketchUp, but Google sold the company, and another company now owns the free 3D wood design software. But SketchUp is still free for carpenters like me.
I think SketchUp is fairly easy to learn, but it has the flexibility to allow you to go a long way in furniture design as your skills grow. It allows you to draw carpentry plans, but it also allows you to see and move around your design in a 3D space. It also generates an outage list. I find it more useful to figure out how to join joinery joints.
Which 20 hand tools for woodworking should you buy first? I wish I could say that the rest is history and now I have a library of hundreds of carpentry plans, but I don't have it. But sometimes a piece of furniture is more complex and requires more detailed carpentry drawings and a list of cuts. I think this last step has made a huge difference in the success of my carpentry plans selling as they have. I had been on my YouTube channel for about a year before I decided to make carpentry plans for a couple of my projects.
I have modified my methods over time, but the basics of how I create my carpentry plans are basically the same.