SSD, HDD installation and backup strategy

Unless you have masses of photos,music there is a flaw in your plan putting photos etc on 4tb you don't have a backup of them. If you leave them on c which should have enough room then create images on too 4tb you then have backup. Best bet is to get Google photo backup app this is free and will backup photos to the cloud automatically and it's unlimited I backed up 75000 for docs save them to Google drive or ms OneDrive again it's automatically backed up. If you created compressed disk images to the 4tb you could get a few backups then your covered even if the PC dies

I would fit a second HD and dedicate this as the backup disk
So it might look like OS is C (SSD), data is D (HD1) and backup is E (HD2)
You would back up both C & D disks to E (say incremental Mon - Sat and Full on a Sun) (don't think the free version does incremental but no matter)
Dependant on the size of your disks/backups you might set a retention policy of two 2 full backup chains for example
If you want to add petitions to D to better manage things then ensure you are backing up disks or if petitions then just add any new petitions to the backup schedule
There is no point backing up to D as if you lose the disk not only lose your data you lose the backup too
I would then go even further and occasionally back up to a removable disk and store this away from home
This will mitigate a catastrophic failure such as flood of fire (you never know!)
Macrium is an excellent program and is well worth the money if you do decide to upgrade (I swapped from Acronis which was truly awful!)

I do this:

1. Create a separate backup partition on your HDD and use this to make frequent images of your system on drive C. I do this to avoid the need to backup this partition on drive D.
2. Backup the system on drive C and your user files on the HDD to an external hard disk
3. Use file history to copy your user files to the external drive.

You will then have 2 back up storage locations for your system backups and your user files. Also, consider making a further full backup to another external HDD stored in another location and not normally connected to the PC in case of ransomware attack or your house burning down!

There are lots of configurations possible with cloud.
Are you looking for backup more for operating system failure to boot, or malware, or drive failure?
Most often the problem is with operating system or partition on the drive.
Another options is to only place the operating system and applications on the SSD and have the User on the HD. All files, pictures etc. will default when saved to the HD. Then you would back up this HD with the cloud or the larger HD.
The operating system can always be reinstalled with a Windows 10 iso or with Macrium.
The applications can be manually reinstalled.