In essence: its ok, it will work as you want, specially if you are giving it such a high priority.
But the correct procedure for that would be to create a script in
/etc/init.d with the correct structure (look for the scripts inside that directory for examples) and issue the command
sudo update-rc.d foo_script.
It will then create links to your script in the specified priority written in the script while maintaining the necessary other services for your script to run. But since your script has a very high run priority and no other services necessary should down up by then you do not need to worry about that.
What you did was just a short cut for what happens using that procedure and it should be fine.