Get rid of the textbox validation border

Easiest way to do this:

<TextBox Validation.ErrorTemplate="{x:Null}">

Set the ValidatesOnDataErrors and ValidatesOnExceptions to False for your binding of your textbox. In case you want your validations, then you have to ovveride the Validation Template for your control. Please refer to my answer here- How to get rid of the red border when a DataGrid cell is invalid?