Welcome Penno! To the forum, as well as to Sony. To truly exploit all the attributes of the a6400, my advice is to not try to shoot with it like a Canon DSLR. Most of our tricks and habits shooting with another (mirrored) platform, will hamper your transition. I had to unlearn some of the things I used to do with my DSLR to discover how much more I can achieve on the Sony.
That was ~6 years ago. Today, your a6400 is packed with even more features. So, I think you're going to really enjoy it.
2nd bit of advice, is to be sure to have a supply of batteries on hand for a full days shoot. Fortunately, 3rd party batteries are relatively cheap these days. I found Wasabi brand to work well for the money. 4 should cover an entire day-night, 6 for cold weather shooting.
Once you get comfortable, explore the potential of very affordable vintage manual-focus lenses. Some have exquisite rendering, and the Sony's focusing features make is so easy.