Suggestions for large DB maintenance i have one large database (more than 1,500 tables and total db size of 56GB) and i would like to ask for tips and guidance regarding the maintenance of such large database!

Will the size be a problem anytime? For example when i reach 4000 or 5000 tables, i am going to have an issue? At the moment i have a "problem" with the backup/restore of it. A complete backup takes around 5 hours to finish, so you can imagine how long it takes the restore! 

As you can understand this is not a proper solution, because in case of a db crash, it will take me at least 12 hours to be back online! Any suggestion?
As your dataset rises, ensure that your active dataset is still mostly in the innodb buffer pool.

As you increase number of tables make sure the table cache can contain all the active tables.

Overall you don't have a large database or a runtime problem but your skills in monitoring have to be in place.

Yes, you have a backup problem, in general look at xtrabackup, replication slave (that you could take offline and copy the datadir), binary logs for PITR (point in time recovery). For a logical backup look at mydumper running on a replication slave.

Tradeoffs are normally infrastructure required vs restore time. Work out your acceptable restore time, a couple of failure scenarios, and run the backup and restore procedure to ensure you are ready.