Measure to display Project IDs based on data in 2 columns.

The below should limit the measure to only show values when there are 3 entries,

Red for 3 months =
VAR StartDate =
    EOMONTH ( TODAY (), -4 ) + 1
VAR EndDate =
    EOMONTH ( TODAY (), -1 )
VAR Statuses =
    CALCULATETABLE (
        VALUES ( 'Table'[Overall status] ),
        DATESBETWEEN ( 'Table'[Reporting date], StartDate, EndDate )
    )
VAR NumDates =
    COUNTROWS (
        CALCULATETABLE (
            VALUES ( 'Table'[Reporting date] ),
            DATESBETWEEN ( 'Table'[Reporting date], StartDate, EndDate )
        )
    )
RETURN
    IF ( COUNTROWS ( Statuses ) = 1 && "Red" IN Statuses && NumDates = 3, 1 )

I'm not sure what you mean in your second question. A DAX calculation can use as many columns as it needs to.

That measure is returning a table of values, so it needs to be used where a table is expected rather than a scalar value. If you are trying to exclude older data from your table visual you could create a measure like

Reporting Dates is in last 3 Months =
VAR StartDate =
    EOMONTH ( TODAY (), -4 ) + 1
VAR EndDate =
    EOMONTH ( TODAY (), -1 )
RETURN
    IF (
        SELECTEDVALUE ( 'Table'[Reporting date] )
            IN DATESBETWEEN ( 'Table'[Reporting date], StartDate, EndDate ),
        1
    )

 and then use that as a visual level filter to only show where the value is 1.

Hi John,

Just to add to this, restricting data to show for the latest 3 months only for which we were comparing data for.
Found this setting in the visual level filter to dynamically show only the last 3 months of data.

So, no need for a separate measure and this actually makes the visual load faster as well.
Just adding it here for others to refer in future.
Thanks !!