Actually, the validation you mentioned (entering string value into a numeric field) is handled by the Framework, not by the grid and it is executed during the CellValidating event.
Considering the first requirement, you may use a RadMaskedTextBox as a CellEditTemplate/ or directly GridViewMaskedTextBoxColumn and define the mask you want to be used. As for the last one, you may perform the logic directly in the setter of the property and throw an exception if it does not pass the necessary requirements.
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