SharePoint Online External Sharing
External Sharing of SharePoint Online - Clarifications
In the above link, it clearly states that – External Users can View / Add / Edit documents.
Also in the below link
It clearly states the below. It does say – that, you can very well do External Sharing with Customers or Clients or even Vendors.
Also in the below link,
It also states, there is no limits on the # of External Users you can share your site with.