Help needed with viable backup strategy please

Barry, I would recommend reading the following Acronis Article with regards to 'Best practice for backup strategy' and using a number of different backup tasks, writing to multiple different backup destinations.

Back up my whole system routinely and automatically (once a month?). Probably to my NAS drive, and/or maybe to my external USB drive. Done a couple of tests and takes a bit under 10 hours to the NAS drive with compression to High, which seems the best compromise. Backs up about 120GB. Done this as a full PC backup.

This is fine but how many disk drives do you have in your system?  Using 'Entire PC' will backup all permanent drives present, so if you have 2 or more drives, I personally would recommend clicking through 'Entire PC' on the Source panel, and then selecting Disks & Partitions and selecting each disk drive to make a separate backup of each using a unique task per drive.  This will help lower the amount of data to be backed up and make any future recovery both easier and quicker.

Compression can reduce the size of the backup file but may also increase the time to create it depending on your processor, memory etc.

Similar to '1', but triggered manually, such as prior to installing new software for instance. I believe this would just mean me manually running the same backup already configured for '1'.

Create a separate backup task to a local external drive then use this for this scenario, keeping your first backup to the NAS running on the defined schedule.  Recovery from a local drive if the new software caused problems is easier and faster than from your NAS.

Have an automated daily backup, capturing any changes I've made to my own documents, pictures, etc. Initially experimented incremental and differential backup strategy for '1', but realise this will soon become impractical. 30 or so incremental daily backup files seems potentially risky, though of course much quicker (17 mins or so). And a 10 hour weekly full backup seems over the top. I also suspect that a differential backup would soon start to take a long time.

Incremental backup version chains should be kept to a reasonable size - the Acronis application defaults to either 5 or 6 files before creating a new Full backup.  The size of Incremental files is much smaller (or should be!) than the alternative Differential method, but the integrity of the version chain depends on having each & every file in the chain with no damage or corruption etc.  A single missing incremental file will break the version chain at that point, rendering the rest of the chain useless beyond that point.  The risk of issues with the chain increase as the size of the chain increases.

Where are your documents, pictures etc stored?  I would recommend considering putting these on a separate partition or drive to your main OS and applications, then having separate backups of them depending on the size of data involved.  Doing any recovery of your OS will require more work if your documents, pictures etc are involved, especially if you have changes to that user data made later than the backup image being recovered from.

But presumably any file history is lost once a full backup is done, which sounds like, with the above strategy, any file history would be limited to 7 days maximum. I would like to retain file histories much longer than that, but not sure how that would work given the above.

No data should be lost by doing any backup activity.  Data may be lost when doing a recovery if that data was not included in the backup archive being recovered from.  I have never used file history so cannot advise on where such data is stored and whether would be included in your backup or not?

And then just suppose disaster struck, and needed to restore everything back onto my laptop. Would it be viable for me to restore from my last Full PC backup (which might be up to a month old); do whatever windows updates needed doing; then restore from my personal files backup from the previous day. Can the two different backups be restored independently in this way, or would the daily backup somehow be reliant on the system being exactly as it was the previous day?

There are key differences between recovering a disk & partition backup compared with recovering files & folders.

Recovery of disk & partitions will wipe clean the target drive as the first step in order to recreate the partition structures from the backup image, so everything will be put back to how it was at the time the backup was created.

Recovery of files & folders can be done to the original locations of that data and will overwrite the data already present, so could be done after recovering the OS at a disk level.

Having your user data (documents, pictures etc) on a separate partition(s) to your OS & applications would make any recovery far simpler.

Example: If the C: partition contains all your Windows OS and applications along with user profiles and configuration.  Then this can be recovered independently to any other data partitions that you have on the same system, i.e. D: partition containing your documents, E: partition your pictures etc, all being backed up separately.  The data partitions could also be mirrored to any of the available Cloud server solutions such as OneDrive, Google Drive etc.

Many thanks. I'll need to digest this and come back a little later. I do only have one physical hard drive on my laptop though, with C: partition my main one. Also D: which is the Lenovo recovery partition. Not even sure if I need this if end up with full recovery facilitated by acronis?