Oh I start with cubes all the time, but usually I just do a new "sculpting" file and it starts with a sphere. But I guess it really depends on what I'm making, sometimes I'll just throw prims in and block out some odd stuff, remesh it, sculpt, and just make some strange odd things. It's all good fun.

And there's no real wrong way to make something really, it's just kind of like, how easy do you want it to be in the end or how few of steps so you want to take. I do tons of stuff wrong and I don't really recommend it but I also don't mind since I'm learning that way! :)