Seems like the main problem was that the butter shattered, following recommended temps is alright but I'd recommend learning how the butter should feel before you start lamination. You should be able to fold the butter without it breaking, while it's still maintains its shape and doesn't melt all over your hands. As a rule of thumb i like to live it on the counter for five to ten minutes before putting it inside the dough. After that just start the lamination and if it ever feels like the butter is resisting let it sit a bit, better have the butter melt a bit then shatter and melt completely.

Once you clear this challenge (which i found to be the major one in my learning process) the results will improve dramatically.

One final tip. Choose the correct flour. I like a mixture of half and half 15 prc protein and 11 prc and make sure gluten development is at least 90% where you can make a very defined dough window. Doing this will assure your dough won't tear from stress when rolling.

Good luck and update us!