I know I don't have much of an iron to put in the fire with less than a year experience but take it for what its worth.
My vote would be with the patterns from the 2nd post. Buy a pattern to start with and progress from there.
I'm a pretty good DIY'er having made all sorts of things out of wood and a lot of other materials. Leather was and still is a challenge for me, which is probably why I enjoy it so much.
How I layout, cut, stitch, finish, tools... Everything has changed from 7-8 months ago when I started.
When I first started I made a few card holders and thought they were pretty simple and moved on. I recently came back and made a few more and what a difference time / practice makes and how you learn to change the order or your techniques.
Regardless what you decide I wish you the best of luck.
As a side note I may try to make this one myself over the next few weekends..
https://www.etsy.com/listing/616382604/backpack-pattern-leather-diy-pdf?ref=shop_home_active_31&pro=1