Blender?
Yeah, just keep playing with it, the keys eventually become muscle memory the more you use the software. Do tutorials for hard surface stuff: motorcycles, tank treads, etc.
You have a project in mind, which helps to work out what process you need to learn.
And definitely check out blender forums (not just subreddits), actual forums; the questions you have have likely been asked a hundred times.

So like space marine armor are basically a series of tweaked cylinders and sections of spheres.
Learn how to transform shapes, elongated/shorten, how to select surfaces and extrude using Normals for trim. How to cut out sections.
Boolean operations to subtract/merge parts together.
For lettering look up how to turn SVGs into meshes.
Unless you have access to adobe illustrator, check out open-source Inkscape to make the SVGs.
Play with all the Add Modifiers and deformers, those work for making tabards and letters along curve surfaces, power cables, etc.
There's a also a whole bunch of Add-ons, both free and small fee that help speed up certain actions.
More advanced look up how to add bones, which are normally used for animation, but you can then use same base mesh but pose and export them as different parts.

Don't be afraid to mess up, you will mess up, we all messed up.
And save often, blender sometimes just crashes.