Need total number of DataExtension Rows, SSJS only run for 2000 records

I had a Data Extension with more than 4000 records.

In my first query I want to count all my rows in the data extension, than I want to get 10% of this amount.

For example: 4400 records => count of 440.

Afterwards, I want to update a field in my Data Extension for only 440 subscribers. If this amount is less than 500, than I want to update another 60 subscribers.. if the count is more than 500 I want to update exactly 10%.

For example: 6000 records => count 600

I never work with query activity and I tried the SELECT TOP 10 PERCENT, this work for 10% but I don't know how to count the rest to fill the amount to 500

I'm very thankful for help.