counting blank cells in range based on condition using another column

I'm importing and validating a number of data sheets. First thing I want to do is simply make sure there's no missing data and there isn't data where there shouldn't be. Most sheets are simple countblanks on specific columns but I now need to do it based the value of another cell.

For example, where the first column contains B or C, the remaining columns must have data, where the first column has no value only the second one should have a value. Countifs look to be out of the question due to the different possible data values and the number of columns to check.

Is autofilter the way to go, followed by countblank on the columns as necessary? Feels like there is more elegant way. I'm trying to avoid coding loops so I can leverage the speed of the build in functions.

B X X X X
C X X X X
X
B X X X X
X
X
X

Thanks

I get the data validation, but what is the outcome that you seek? delete row? a simle "yes" somewhere in the sheet?

A simple count is fine as it will just be used to decide whether to carry on with validation.

Thanks