Welcome, if you haven't yet, consider joining the St Louis bonsai club https://stlbonsai.com/ they are very active
and I think you learn way more from people than the internet and books, especially what works and doesn't in your climate.
I'm with Will, love the slab the whole composition is coming together nicely, as you know I prefer this orientation, and reining in the yarrow really helps the scale and proportions
I think it all depends on your goals, if you view bonsai as leisure/backyard hobby (like me) you can participate forever without spending much money.
However if your goals include creating showable trees then it will cost something whether it's money for material, pots, and supplies, or many...
I like the relationship between the rock and tree best in #3
#1 could work over time but the tree is too small for the rock currently.
#2 the tree seems disconnected from the composition, like it's floating behind the rock.
Looks like a fun project, can't wait to see what you come up with!
Not the best time to be messing with roots, probably could have left them until spring before separating.
I typically give my seedlings at least one or two years before disturbing them.