I am new in odoo, could anyone please reveal this mystery for me:

1. I have created a product type service, how can i update the quantity on hand?

What i did is make a product first as a stockable product => update quantity on had then => edit product type to service! 

but it seems to me not a legitimate way to do that!?

2. my second inquiry is how to manage inventory of a products type serves, like "subscriptions"?

Thank you in advance!