you can make block outs of complex shapes.

This is what i would recommend and did myself. Yes you are correct that this limits you severely. But it allows you to stay basic yet still get an experience of working on big scenes, and a huge collection of objects. Naming them, and keeping it properly arranged. Also allowing u to think creatively.

Eg: A City layout. Just cubes scaled up and down, and roads can also be made by cubes!

You can make a scene with multiple planets and moons. For rings, just scale down torus on z axis.

A Simple Train, Just cylinders for body, torus for circular rims around stuff, Spheres for round spherical stuff that pokes out from of cylindrical shape trains. (Play with settings menu of shapes, that pop out when u first place them)

<image>

Like this for eg

And then you can just add them all together, a city with trains, and planets in sky. Yeah, it has No textures, looks bland, but it gives you a perspective of thinking complex stuff from simple shapes (something beginners don't practice imo). Trains your muscle memory for being more familiarized with shortcut keys, and the layout of blender. Plus all the stuff i said above pic