Hi there @Westfamily I thought I would respond real quick since I purchased the Simple Machines for my 6 year old boy who is also in 1st this year 
We are getting ready to start this set in a few weeks but I have looked over the teacher materials pretty extensively and am excited to get started! Here are links to what we purchased and it is everything you would need for this set:
Here is the link for the actual lego pieces for this set:
And here is the link for the teacher materials (referred to as the Activity Pack):
https://shop.education.lego.com/legoed/en-US/catalog/product.jsp?productId=2009689
And here is a link for both the student legos and the teacher materials all together in one large set:
https://shop.education.lego.com/legoed/en-US/catalog/product.jsp?productId=5003466
I ordered directly from these links. I hope this is helpful as you are thinking about this purchase. If you have any questions about it, feel free to send me a message and I’d be happy to answer them since I have the materials here and could glance through the teacher guide/materials and send along anything that might be helpful. The prince is somewhat steep I thought, but the lego set is actually meant to be shared by two students working together (although it can be built by just one child working independently also). My son is actually going to be doing this with a buddy who is coming over on Mondays to do Lego Lessons with him and he’s really excited. I hope these links will be helpful!
As far as the Jr. stuff, I didn’t look at that as much–these lessons/materials in the Simple Machines set look to be right on target with my son’s age level. I will say though that he is reading and starting to write somewhat/fairly independently although I do write for him sometimes when he gets tired and he narrates his answers to me, so I can see that happening sometimes on the worksheets that comes with this set (in the Teacher materials). Again, feel free to ask any questions and I’ll be happy to try to answer anything if I can even though we’re just getting ready to start it ourselves!