I need a bit of advice on a Batch file If exists then followed with a loop

I am trying to create a batch file that copies files from one folder to a new one that it creates (mkdir "new folder") and renames the folder "1". If folder "1" already exists then name it folder "2". This would loop by adding 1 to the folder name till that folder did not exist and then copy the files to that folder. Here is my code so far. I have searched the site for some direction, but am not finding anything specifically doing this. Any help would be much appreciated.

* The areas I need help with are set in the program with :: comments *

@ECHO OFF

cd c:\

set a=1

mkdir C:\"New folder"

ren "C:\New folder" "%a%"

:: if the folder already exists then

set /a "a=%a%+1"

ren "C:\New folder" "%a%"

:: I need this to loop till the folder does not already exist and then can be renamed.

:: Then I need to files located in "c:\folder_to_copy" to copy into the newly named folder

robocopy "c:\folder_to_copy" "c:\%a%"