How many channels allocate for taking backup on 5 TB database

Hello,

We have 5 TB database with 10 core CPU and 39 Gig Memory on the server. Below is the channel/command and configuration which we used to take backup. Please let me know how long it will take time for backup the 5 TB DB approx. and If we dont have have full backup, can we restore the DB with below incremental backup method/configuration.?

allocate channel ch3 device type disk format 'xxxx/%U';

backup incremental level 1 for recover of copy with tag 'daily_bkp' database;

CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 7 DAYS;

CONFIGURE BACKUP OPTIMIZATION OFF; # default

CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO COPY;