Let's go by parts:
I want to add the stock info of my suppliers to my woocommerce website. I want it to be if that my supplier has 6 in stock, and i have 0 that my backoffice says my supplier has 6 in stock
You can do this with our Premium add-on ATUM Multi-Inventory. If you have two inventories, one can be yours and the other one for the supplier.
my frond-end says that the product will be available the next day
This can be achieved with custom development, but as we don't offer this service you will need to hire a developer.
And my suppliers have a daily CSV export and some of them have a URL i can upload with stock information. So that is where the information comes from.
You can do this with our premium add-on ATUM Export Pro. Currently you can import CSVs of the supplier manually, importing from an URL is in our roadmap and will be available in a future version.
Hope this helps,