Hi, 

It looks like you have a few signs and symptoms going on here. The branches with a split in them is old cicada egg laying damage. You can prune at out of the tree as it will cause some branch die back. 

The brown flowers and leaves appears to be brown rot. This is relatively new to flowering cherry trees and there isn't a specific treatment that is recommended at this time. You can try to also prune out the infected stems to the healthy sections. You may want to try a fungicide spray even for ornamental cherries. You can search for a product with the active ingredient 'myclobutanil fungicide' usually it will be called Spectricide Immunox (most easily obtained for home owners - however an internet search could lead to other brand names). You will want to read the label directions carefully and make sure you have proper equipment and PPE (protection) before applying. Also make sure the label lists for ornamental cherries, but from our research it shows that it does. If you feel like this is too tall and you won't be able to get proper coverage, you may want to consult with a certified arborist or a certified pesticide applicator as they would have the proper equipment and PPE necessary for reaching the entirety of the leaves and branches.

Finally the holes in the leaves look like cherry shot hole fungus and usually don't warrant any treatment unless there is a significant amount and it is causing branch die back, but it looks like you should focus on the brown rot first. 

Let us know if you have further questions with this information. 

Emily