So....you want to get started with some challenges. Good for you! You are not alone, and the more you get into using challenges, the more confident and excited you will become! And be excited with the students as you try out new resources - the students will love your enthusiasm!
One piece of advice is to allow yourself to learn with the students - don't try and be the expert! When we started coding with our students, we involved our Board's IT department, and asked for help with the first steps. Then, as the students learned, we learned with them.
Another tip is to document your learning as you go, so that you can remember any challenges you overcame the first time, and then your next class will have a smoother ride! Don't be worried about bumps in the road - scientists learn through failed results, and your classroom full of scientists will do the same.
Letting go of your role as the 'Expert on Everything and Giver of Knowledge" is crucial in setting up a classroom full of STEM challenges - you never know what will happen, and you need to be ready to learn as you go, just like your students! When I set up lab demonstrations and science fairs, I make it clear to my students that I am not the expert on every subject, and that they will be teaching me things too!
Set a stage for active science and technology in your class by using my 'Science Class Expectations" document in the resource section (or something similar) to ensure your class has safety measures in place. The best way to provide a rich learning environment for STEM/STEAM is to ensure the safety of your students by going through scenarios and teaching them how to properly use equipment (I can't say enough about how important safety goggles are).
My best advice is to start small - start with one challenge in each term or during a unit that you would like to start with in science as part of your regular science curriculum. Start with your first challenge that is pretty much designed for you and your students such as using a challenge from one of the following resources: