1) The Drobo 5C has only one USB-C port, so you can't connect another 5C (daisy chain-en). The 5C has five hard drive slots that can be occupied. At least two hard disks must be present, but then you cannot set up a failover of a disk. I have installed five enterprise-grade hard disks of 4 TB each, which gives me a capacity of 14.34 TB with failover of one disk. A maximum of 64 TB is possible. (When setting up the 5C, you can also choose to have a failover of two hard disks, but this is again at the expense of the available capacity). The failover allows a defective hard disk to be replaced and all data to be restored. That's why I would call another network data storage overkill.

2) I would assume that if you have a backup software solution on your Mac, it will "monitor" the source directories on the 5C and move any new additions to the 5N2. In this case, your Mac would be the operations centre. Certain external data storage devices can be set up to carry out this forwarding in the background, i.e. data storage device to data storage device, which is not possible with the 5C.

1) The Drobo 5c works like an external hard drive. If a second external hard drive is connected, you can easily make a backup of the Drobo on it.

2) Everything you can do with any hard drive (e.g. save to a network drive) can also be done with a Drobo 5c.

In principle, however, it makes no sense to make a backup of a Drobo 5c, because the data on this Drobo is already backed up twice. If one of the 5 hard drives fails, no data is lost. You insert a new hard disk and the Drobo distributes the data again so that no loss can occur. It is highly unlikely that all the installed hard disks will fail at the same time ...