I learned by watching videos, reading everything I could get my hands on, talking to everyone at quilt shows, etc.
What I learned is that there are literally hundreds of places free and paid classes, books, retreats etc available now to learn from.
First of all, your batting will give you a recommended quilting distance necessary to hold your quilt together without the batting clumping up or migrating around.
Once you get beyond that, it really is up to you to decide how dense (or not dense) you prefer. You get to choose whatever design or combination of designs you want to try.
And as you get more and more comfortable with your machine and your growing skill level, your tastes may change. You may find that you love using stencils, but hate ruler work. Or you love playing around with random shapes and motifs. You may want to challenge yourself with feathers or precisely measured and marked geometric lines or circles.
It really is all about what you prefer.
It is true that the more quilting you do, the closer together and small your designs, the more dense you quilt a piece, the stiffer your quilt will be. So if you want fluffier, less stiff piece, then go with a large design that spreads out and isn't too close together. If you want to highlight a specific area, close, small quilting around it will allow it to 'stick up' above the surrounding area that is sort of mashed down by your quilting.
I would suggest you practice on some large scraps, play and test out some motifs you want to try.
You can also draw a design you're considering on a sheet protector, or anything you can see through and lay it over the area on your quilt you want to work on. A way to "see" what it will look like and how it may fit first before committing.
It would also help if you could find a quilting buddy to practice with & bounce ideas off of.
You can find designs, motifs, and ideas everywhere.
Some more good videos to find and watch:
Jenny Doan
Pat Sloan
Lori Kennedy
Leah Day
There are so many more!
https://www.craftsy.com/post/free-mo...for-beginners/
https://duckduckgo.com/?q=free+motio...=v314-1&ia=web
wish I could be more help!
love your stencils.