Multiple Organisations - 1 account or multiple accounts?

Multiple Organisations - 1 account or multiple accounts?

Hi  Sorry if this has been asked before, but I can't find a recent post on it.  I have approx 20 customers, at the moment.  They all have access to online documents at the moment through sub-domains on my website.  I would like to migrate these to Zoho and manage these customers/docs using Zoho Docs in future.  Some of these customers have databases too, so I would like to include Zoho Apps as well.  It seems to me that it would be much easier to manage this situation through one account.  Is this possible/allowed please?