I think this can be done using a 2 step process
1- Create a random number
https://community.quickbase.com/quickbase/topics/is-there-a-way-i-can-generate-a-random-number-for-m... and populate the key field with the random number using a form rule
2 - Create an action or automation that changes the key field to the value of record id # + 1000 any time a record is added
If you choose to use an action you would need to create a report link that connects the record to itself (I do this all the time). With automations you can create trigger when a record is added for the record to update itself.
Good Luck :) let me know if you need any more help on htis