My question is: what are some great resources out there?
Of course there are the docs themselves. And the come back stronger materials (and EPi courses in general) are great.
I've recently just bought and finished reading through Jon's The Missing Manual. I thought it was great. I really enjoyed how Jon not only walks you through how to do something, but he explains why and also provides alternate approaches whilst providing his thoughts on the pros and cons of each approach.
As someone who only has ~4 years of EPi (and C# / .NET) experience, I am very aware of the old saying "you can't know what you don't know about' - or words to that effect. I'm currently working my way through Mark J Price's 'C# 9 and .NET 5', which is the second book of Mark's I've purchased. Whilst not EPi specific per se, it's been great for broadening my understanding of what's achievable which is scratching the itch nicely.
I don't work with Commerce right now, but at some point I will most likely pick up a copy of Quan Mai's commerce related material.
So yeah, any other recommendations from anyone?
You can go for some of their training
and play with code examples from their Github repo
For me, Episerver & Episerver dev's Github and Blogs are the biggest sources of learning.