Sorry it took me a bit to get back to you.
I understand how you feel when it comes to thinking about doing art or work, and hoping or feeling like I can do that, but then feeling disappointed when I don't match my mental vision.
One of the biggest things that helped me most in starting to understand and learn art was to be okay with making shitty things. Be comfortable fucking up sometimes, it's okay to make something imperfect, even if it feels a bit frustrating.
Getting more comfortable with your creations can take time, but it is something you can learn, and I have confidence you're able to as well.
As for actually getting into the 3D modeling and sculpting itself, the main trick which helped me a ton was to just start blocking out models first. idk if Nomad allows you to make primitive shapes and combine them, but the blockout step is super important to me. It lets you get some idea for proportions and shapes of the reference images. Keep your eyes out for big shapes in the objects you're referencing. It can be hard at first, but it's a great skill to have.
Additionally, figuring out the shapes of the objects you're referencing is a great way to be able to use any image as reference, and not needing a perfect character sheet from all angles.
Keep trying, and do your best, even if you feel like it's not good enough. Keep your eyes out for cool techniques and things you might stumble across in the process, and learn from each project.