SQL Query:

WITH TopApplicants AS (
    -- Step 1: Find the top 10 applicants by total product count
    SELECT
        applicant_full_name,
        COUNT(*) AS total_product_count
    FROM orange_book_products
    WHERE applicant_full_name IS NOT NULL
    GROUP BY 1
    ORDER BY total_product_count DESC
    LIMIT 10
),
ApplicantRouteCounts AS (
    -- Step 2: For the top applicants, count the occurrences of each route
    SELECT
        ta.applicant_full_name,
        p.route,
        COUNT(p.id) AS route_product_count
    FROM orange_book_products p
    JOIN TopApplicants ta ON p.applicant_full_name = ta.applicant_full_name
    WHERE p.route IS NOT NULL
    GROUP BY 1, 2
),
RankedRoutes AS (
    -- Step 3: Rank the routes for each applicant based on their count
    SELECT
        applicant_full_name,
        route,
        route_product_count,
        -- Assign a rank to each route within an applicant, 1 being the most common
        ROW_NUMBER() OVER (PARTITION BY applicant_full_name ORDER BY route_product_count DESC, route) as rn
    FROM ApplicantRouteCounts
)
-- Step 4: Select the most common route (rank 1) for each top applicant
-- and include their total product count for ordering
SELECT
    rr.applicant_full_name AS applicant_name,
    ta.total_product_count,
    rr.route AS most_common_route,
    rr.route_product_count AS count_of_most_common_route
FROM RankedRoutes rr
JOIN TopApplicants ta ON rr.applicant_full_name = ta.applicant_full_name
WHERE rr.rn = 1
ORDER BY ta.total_product_count DESC -- Order the final result by the applicant's total product count
LIMIT 20;