How to store customer data?

Question

Information Security

Good time!
I create websites, mainly for small and medium businesses.
The customers are all different: someone will be satisfied with registering a domain in my name, someone doesn’t mind if I register it, but through my account, and someone fundamentally needs 100% access to their account with the registrar (and don’t care what I will renew the domain, they just need all the access data and full access itself out of principle).
Many sites have an admin panel, which means that you also need to somehow store a couple of login and password for it.
Mail for the domain, metrics, direct, webmaster - you also need an account on Yandex ... +1 login-password pair.
In general, I have to store a lot of data about each customer ... Why store it? Customers are like small children - they constantly delete letters in the mail, they are too lazy to scroll through the dialogue in VK, they forget, and so on ...
For many services, you have to store answers to security questions, code words and other nonsense. You never know.
How can I properly organize the storage of passwords and data?
In a notebook - not practical and not very safe.
In Excel - my ssd will die and that's it ...
In an Excel file and throw it on the cloud? How safe is it? Do I need to encrypt the file, and if so, how?
The solution should be simple because I work on a computer, tablet (on Windows 10), and sometimes even from a smartphone (Lumia 950).
I'm sure someone has already encountered this, tell me, please.
UPD. I remembered that I use the VKarmane application (encrypts and synchronizes important data: documents and notes). Yes, it's cool and convenient. But another moment appeared ... If the service is covered (everything is possible), I will be left only with the encrypted database and that's it. Stop, dumb. The data is stored locally, it is only backed up to the cloud. Therefore, even if the application is removed from the store, it will not be deleted from the device itself, which means that I can overtake everything to another place. But if someone advises a more beautiful solution, I will be grateful.

Answer 1

1password or keepass.
The database of logins and passwords is stored locally and synchronized to the dropbox.
The database, of course, is encrypted, opens with a master password.
Bonus are browser plugins with autocomplete and the ability to access the database from a mobile device.