Help to configure my system

Hallo
I’am trying to imagine how to best configure the hardware I have to work with OMV

Nas:
HP N54L (12Mb RAM, 4+1 3,5 hot swap bay, 1x2,5 bay)
Qnap TS212 (2 bays)
HD:
4 x 3TB WD red
2 x 1TB Seagate
some external USB

My goals for the system are:
Safety: I do not want to lose my files!
Scalability: If/when I do need more space, I do not want having to rebuild anything, just add drives.
Automation of backup: I know myself and i am sure I’ll sometimes forget/postpone to make a backup. And it will be when a crash happens!

So this is my thinking:
PERSONAL and WORK FILES that are stored in PC, laptops, iPad, Android phone etc.
-Sync to shares in HD01 in the N54L.
- This disk (HD01) is synchronized to HD02 in the same N54L.
- Both disks backup to two hd in a Qnap TS212. Disk 01 to disk 11 on odd days, and disk 02 to disk 12 on even days. This way I always have two backups: yesterday and the day before.

MULTIMEDIA (movie, music, photo): stored in HD03 in the N54L
- This disk (HD03) is synchronized to HD04 in the same N54L.
- Once a week/month, backup to an external HD.
I have not yet investigated abt how to have access to these files through my devices.

Notes:
PC drives have NTFS file system, for compatibility both with Linux and Windows,
Backup drives have NTFS file systems too, for immediate access (in case…)
Nas HD have EXT4 file systemNo ZTFS or Raid for safety questions
The Qnap will be stored at my mother’s, connected via wifi (50 metres).It wakes up at midnight and shut down automatically after backup done.
The external HD will be either a USB or Esata, plugged in just for the backup and then stored away. Maybe I could rotate two HD

I have made a sketch to better explain the configuration.

I would like having your opinion and your suggestions.

@'David
3TB hd will be HD01 HD02 HD11 HD12 i.e. "Personal and work file" hd in N54lL and both Qnap backup hd
1TB hd will be HD03 and HD04 i.e. "Multimedia" hd in N54L. I'll upgrade them if/when I'll need it.
sorry not to have explained it before, I wrote it in the sketch

I wasn't aware of this problem with NTFS. Do you think using Ext4 for backup disks is a better option? In case, I could access to data with Linux

I know backup will be slow via wifi. I am planning to connect the two houses via ethernet cable in the next few months.

thank you David

@'David
Honestly I don't need so much storage either for my files or for Multimedia, but these are the hd I have. My files will have some changes every day, this is why I decided to have a daily backup, therefore I assigned the 3Tb hd to them, not to mix 1tb and 3 tb hd in the same group. Multimedia will have less changes, so a weekly or even monthly backup will be enough. Do you have any better idea about their use/configuration?
i'm realizing that, while I have a double backup for data files, I have only one backup for Multimedia.

I think I have no privacy need for photos. I'll give access right to multimedia to my family members only (group family).
I am now realizing that, while I have a double backup for data files, I have only one for multimedia, therefore storing photos and other valuables together with data files could be a good idea. But I'll love to have them separate..
I have no solution in my mind!

just an other idea:

4x3TB hd in N54L as follows:
HD01: personal files (syncro from PCs etc.).+ Multimedia (file server)
HD02: mirror of HD01
HD03: backup of personal files on odd days + backup of multimedia on odd weeks
HD04: backup of personal files on even days + backup of multimedia on even weeks

2x1TB hd in Qnap (to be upgraded to 2x3TB if/when needed):
same as HD03 and HD04
placed in different location (mother's)
what do you think about this?