The page size is 500, that's why your result set is split into 3395/500 -> 7 pages.
You need to issue 7 calls to Dynatrace API to get the full result.
You may want to try the pageSize parameter to return larger pages, but 5000 is the maximum anyway.
No you just copy the nextPageKey value, remove all the other filters and just call the same endpoint giving only the nextPageKey as a cursor. You will then get the next 500 entities and a NEW nextPageKey that you again enter as the cursor.