>I'll use up all my good ideas on practice comics. Thoughts?
1) Your ideas are likely not as good as you think they are
2) You will likely gain a lot more ideas as you start actually creating and not just daydreaming about it
3) You learn a lot about visual storytelling along the way and can always go back and revisit and refine old ideas
Don't get me wrong, you can definitely hone your art skills without working on comics, but comics are so much more than just the art. And even the artistic aspect of comics may differ from what you'd draw for coom. Becoming a great pin-up artist doesn't make you a good storyteller and you will struggle with simple things such as panel composition and drawing backgrounds. So if anything you'd do a lot better practicing illustrations, but even then you're missing out on writing, paneling, typography, etc
If you want to draw comics, draw comics. And start with one-shots. If you can't tell a story in 6, 12, 24 pages you won't be able to keep up with a long running comic. So start with small projects, get better at drawing comics and maybe even build the foundation for an audience. If your comic is genuinely good people will read it even if the art isn't your strong point.