I want my add- on to start running as soon as the raspberry pi is started and I also want it to run it in background how can I achieve it ?
We believe this is a Kodi issue or a specific Kodi function and as such you should look at addressing the issue there. If you do believe that this is an OSMC specific issue, please let us know.
Your question may be explained in the Kodi Wiki. Have a look at http://kodi.wiki. This should be your first port of call for Kodi related questions.
Make it a service add-on.
How can I make it service add-on ?