large scale reliable software system using PostgreSQL

Dear all,

After greeting,

I taught PostgreSQL myself and developed a small scale experimental
software system using PostgreSQL in the back-end.

I would like to know your advices to develop a large scale reliable
software system using PostgreSQL in the back-end, through which i can share
the storage with the different system users where they login to the system
through the web application front-end with different passwords and user
names , save the privacy of each user data, achieve overall system
security, achieve fast response, make backups and save the stored data from
loss. The system will be hosted on a cloud.

Thank you in advance.