Well there is a difference between artistic skill level and technical skill level. You could be a great artist but spend a year learning how to be a great modeler. Longer to be real exceptional.
I am an advocate of project-based learning. Where the goal is creating something awesome.
Before I started learning Blender I had already been a modeler for a good number of years. So when I started learning Blender I had no need to work on projects right away. I just spent the first month learning and doodling.
Then once I had the tool under my control I started doing creative projects.
When I first started modeling a good number of years ago. I pretty much approached it the same way. I got in there and learned the technical basics first. Then I started creating - like crazy.
And for me it is the combination of being competent at what I do, understanding the fundamentals of what I am doing before I get creative. And if I have to learn something new, or run into a catch, I immediately shut down the creative project, open a new file and first just start to understand the thing from its basics. Then once I have it, I go back to the creative file and apply what I know.
This is what I mean about managing your time and objectives.
As far as project size or scope. I don’t think it really matters. You could take a year to make an open world if you want.
Every project no matter the size is going to be broken up into smaller tasks. Team or one guy. Same thing.
I think you will be OK as long as you are creatively happy. And if you want to take on a magnificent project with an awesome scope. Go for it.
Just make sure and understand there will be a constant balance with learning (not being creative) and creating. And I think it is best to manage your time likewise.
For instance, for the next two or three days I am going to learn everything there is to know about particles and physics. Then when I am done, I am going to go and make some awesome grass.
But lets say you have not learned how to use Cycles yet. Well that grass is never going to look awesome until you can render it. So, go off and spend a week or two playing around with cycles. Then come back to your master piece grass project for your temple.
I am just tossing things out there. But you know what I mean I think.