I enjoy the doing aspects of bonsai, the horticulture gives me pleasure, I enjoy it even if most of my trees are not what would be considered "good bonsai", they are all in some phase of "becoming bonsai". Its the process I enjoy, getting a "finished tree" is the end goal, but the enjoyment is in the process for me.
I have been dabbling with bonsai for 30+ years, the first 20 I was at best a dabbler. At some point a decade ago, I looked at pictures I took of my trees, and saw that my trees looked like sticks or shrubs in pots, not bonsai, not an image of trees in nature, no visual, emotional or artistic impact. That's when I decided to join a bonsai society and take some classes, because I was clearly missing the point. Now, I have a collection that looks like a collection in early stages of becoming bonsai, but definitely with much more potential than my collection 20 years ago. My early attitude, 20 years ago, was I knew enough from books and inter1net. Now I realize I needed hands on in person instruction. Now I think I am getting it. If at all possible, attend at least a few meetings a year of a bonsai club, or attend a show, take a class, get some hands on if you can. Even if it is only once every couple years, but try to get some hands on instruction. Just a suggestion. It might be quite difficult given where you live.
You are right, what you know about growing nursery trees is critical, it really helps. Young tress, or trees early in bonsai development are treated more like nursery trees than anything else. There are bonsai specific techniques applied to nursery stock, but what you know about keeping nursery trees healthy will greatly help you with bonsai, most of the horticulture is the same.
A caution I'd like to share, as it was a mistake I personally kept repeating the first 20 years of my journey with bonsai, I kept applying technique for near finished trees, getting ready for display, to stock early in training. Most of the articles you read will be about the techniques for preparing nearly "finished" tress. There are far fewer articles about training early in development material, you need to keep an eye out for these. These are the articles that will help you develop your bonsai the most. A start is the articles written by Brent Walston, at Evergreen Garden Works. Brent specializes in raising young stock and preparing it for eventually becoming bonsai. I also have bought many of my trees from him. His grafted pines have uniformly good low grafts, excellent material for becoming bonsai. He also propagates many tree cultivars from cuttings, and prunes with intent for them to be used for bonsai.
http://www.evergreengardenworks.com/articles.htm
I really hope you go back and get some of the old, but still tiny pinion pine seedlings. Because they are small, you will have a better chance of getting enough roots that they will survive the collection process. Then get them established and growing. Some great pines that are on the show circuit in Japan were indeed raised from seed. Look at articles on raising Japanese Black Pine from seed. You will see that in the nursery can, or planted in a grow bed, they allow the trees to grow out, to maybe 5 or even 10 feet, then cut back to the 8 or 10 or 24 inch tree they had in mind, then select certain branches to grow out again to 5 or 10 feet, then cut back again. So if collecting a 10 foot pinion is not possible because of the long roots, collect some small pinion, use a cycle of growing out and cutting back like they do with Japanese Black pines to get the large trunks, with good taper, and trunks with interesting changes in direction. I think pinion is one of the USA native pines that has good possible use in bonsai. And it is native to your area, Go for it.