Sketch Up is cool, but it's a program that only does a few things. It's primarily a cad style modeler. There is a free version, but the fuller featured PRO version with all the better stuff costs 500.00$. And that doesn't do even near the amount of things Blender will do.

Blender does almost everything. Modeling, Texturing, UV Mapping, Baking, Sculpting, Rigging, Particles, Physics, has 2 built in renderers, node based shader editor. A GLSL shader mode. It also does animation on the whole scene/timeline, or action/clip based (useful for games when you make animation clips for characters (walk/run/attack/etc...), and anything else you want to script in. It also has a scriptable game engine if you want to prototype some ideas there. It's like a swiss army knife of graphics programs.

Most of your time in Blender, you will use only 3 keys. G(grab/translate)/S(scale)/R(rotate). You don't even need to use keys for those, because you can use the transform gizmo (which is usually less helpful than just using the hotkey. You'll mostly disable the transform gizmo anyways).

The hotkeys change depending on what mode you are in, because everything you can do in 3D modeling is context sensitive. Object mode commands don't make sense in Edit mode. Edit mode commands have no place in the sculpting mode, etc... But it doesn't matter, because everything a hotkey can do is also in the context menus, the menu bar menus, or the space bar menu.

Blender's hotkeys work just like any other program. You don't have to learn them if you don't want to, but they are there to help you, and you much better off using them. Just like no one uses the menu bar to do File->Save(Ctrl-S), Cut, Copy, Paste, etc in any program. And we have Function keys to compile and run or debug. The menu bar just slows you down.

The same goes for making artwork 2D, 3D or otherwise. No one (who knows what they are doing) wants to stop using the mouse while they are in the middle of creating something because you always end up with ugly, jagged, results. Trying drawing a circle on paper where you keep lifting the pencil every few degrees. You get a jagged mess. Letting go of your work to click on commands in menus interrupts your smooth flow, and your thought process.

Once you get the hang of your program of choice, you are going to start using it at a different level. You will have one hand on the keyboard, and one on the mouse or pen, and the program will disappear. You won't be thinking in terms of hotkeys (that's muscle memory) or mouse movements anymore. You'll be thinking in terms of what you are creating straight from your head to the screen, and getting actual work done.

Blender, GIMP, Inkscape are the Open Source hat trick. If you learn those three well, migrating to other platforms later will be fairly easy and all of your skills will be useful on both commercial and free software.