The obvious remark is why do a new webapp deployment per customer instead of a multi-tenant app ? Multi-tenancy requires more code in the web-app to isolate accounts, but it will mutualize and consolidate web servers.
I did it because a new webapp deployment costs nothing, no extra work involved at all with DO, just add a snapshot and ssh key to a new droplet. If something needs to be consolidated, I just use DO api and paramiko to ssh into each droplet and run new commands. If it's updating the webapp across all customers, it's a matter of issuing restart command to all the droplets via API.
Aren't you paying for hosting on each droplet though? Consolidating would save you that money, but I guess this wouldn't have a huge impact if the income per customer is a lot larger than the cost of an additional droplet.