I'm about five years in and still consider myself a newb. Each time I get into a new species my newbi light shines brighter. New is a relative term compared too... I suppose beginner or intermediate is really where I'm at. I love this hobby and thread.
I'm posting to offer some advice, not on individual trees but about the journey. Mainly the mistakes I've made and years/trees I've wasted.
Don't rush them into a pot too soon. I still do...
Don't try to learn 30 different types of trees at the same time. Still doing it.
Don't base your collection on seedlings exclusively, especially if you are near 60 and impatient as hell.
Don't spend a ton of money right away unless you have 5 tons of it laying around to spare.
Don't expect instant gratification unless you buy finished tree which you will likely kill. Back to the Ton$
Don't get too many trees in relation to the time you have to care for them. Overwhelming
Don't try to grow zone 7-8 trees when you live in zone 6. Grow zone 3-5 making winter less stressful and spring less sad.
There are many more don't you will discover and more I could post.
Do have enough trees to keep your itchy fingers busy so you don't "love" the few to death.
Do your homework here before you post questions as so much good info is already here.
Do join a club nearby if you have one. Mine is an hour away and on Sunday afternoons I don't like to spend indoors in summer. I've been to a couple meetings but should go more when we get back to having meetings.
Do dig trees and plants with good trunks but only after doing your homework. I have killed 2 spectacular trees collected and still feel the remorse.
Do listen to the many advanced people here who take their time to offer you advice and follow it. Leo, OSO, VanceW, Adair, Judy and several others are solid. Put smoke on ignore.
Do look constantly for landscape projects and demolitions for older specimens to save you years of development.
Instant Bonsai isn't really possible but there can be accelerated bonsai.
I'll post two trees I dug from a yard just last spring for encouragement. These could be called rushed bonsai for the impatient. Enjoy the journey!