I’m also very new to leather work also. All these tips are very good. I agree with buying a pattern and learning how to make it. Look for patterns on Etsy that have construction videos. I’’d suggest finishing the piece even if you mess up a stitch line or have a weird cut. There are several techniques that u learn from working a project from start to finish.
I’ve messed up so much stuff but also have learned several skills along the way. I’d suggest getting a small card wallet pattern or something easy that u can build skills on.