"Yardadori" (depending on the species) are good to practice on coz it's free. Let it regain its health first (for about a year depending on its health) before you do any hard wiring coz that's stressful for the tree. The general rule (to be on the safe side) is to do one insult a year but depending on your experience and the tree's health, you can do both in one year without any problem. I certainly did this 5 years ago all in one season (light root pruning, heavy foliage pruning and heavy wiring with some jins here and there) and all 4 juniper trees are thriving well. Juniper trees are very resilient at least in my case. For the most part, it's always about the health of the tree first before we do any aesthetical intervention.
Also, it is best to look at bonsai qualities before you collect anything. Not all collected trees can be considered "Yamadori". It has to have bonsai qualities to be considered one. Although, the meaning of the word means collected tree but in Japan (when I visited some nurseries ages ago), the term "Yamadori" isn't given lightly. It has to show some great bonsai qualities to be considered one. Since then, everytime I see pictures of "Yamadori" here in the US, that's the first thing I look for and honestly, not all have very good bonsai qualities (can be subjective). You can Google "great bonsai qualities" and that will give you a general idea.
Anyway, enjoy the journey. This taught me patience ever since I started this hobby over 30 years ago. Bonsai is all about patience and doing things the right way and at the right time. Get more books, research online and watch videos - It'll help you a lot in your journey. There is Mirai as well..they have some good modules that you can check out. It is normal to make mistakes and possibly kill a tree. Don't let that discourage you but let it be learning lesson. Even after 30 years, I am still learning something new. It almost feel like it is an endless journey
* get to a local club too and maybe have a sensei to teach you a thing or two..that'll expedite things for you as well. Good luck.