No gaming and (presumably) no video editing: then anything with a CPU running over 3 GHz and more memory than 8 GB is definitely unnecessarily powerful. Even if you run highly inefficient software like Microsoft Office and likewise behemoths.
Similarly you shouldn't need a separate graphics card if there is on-board motherboard graphics. If your keyboard and mouse are still going strong you shouldn't need to buy something "included" with a new PC.
On the SSD: check for those with a "M.2" interface rather than SATA. They're supposedly faster (do not have one myself though), but OTOH more expensive.

Make sure you can easily remove (and reinstall) the hard disk. Preferably be able to install another hard drive, so if possible make sure there is a spare power supply cable and a SATA cable included. You don't want to hand out your private data files if your PC needs to return for repairs.

That leaves a lot more options. Whatever you save here could be spent on a better (larger? UHD?) display. Just suggesting.

On reliability: one always runs the risk of a "Monday-morning produced" set. So go for a brand that is known to be reliable AND with a good and serious guarantee policy with both your retailer and the brand. Take a retailer with an in-house tech department -- you wouldn't want your PC gone for weeks because it's sent to the manufacturer.
I would prefer Windows 10 Professional over the Home version, because of the options. Even though it costs more.

On a final note once you have the PC
As with every windows version to date (and I have used it since 3.0 ...) there are some weird defaults to alter. Be sure to relocate your swap file to the hard disk, so it is not on the SSD. Similarly, the 'Documents', 'Downloads', 'Music', 'Video' and 'Pictures' are by default on the same drive as Windows, in other words the SSD. Relocate them to the hard disk (right-click on "Documents" (and so on), select Properties and then Location, then Move....
A good brand/retailer may have switched this already for you, but be sure to check.

Agree on:
- no graphics card needed (increases cost, temperature and noise for nothing)

Partly disagree on:
- moving the Own Files/Pictures folders to the hard drive (especially with photo browsing this is annoying...)
- 3GHz is enough (the more the better)
- 8 GB RAM is sufficient (Depends on the applications used; photo editing, everything with 3D or graphics tends to use everything, which is available; just check, if your current PC uses more than 6GB - if yes, 16GB are worth an investment; but with current memory prices it is really becoming an issue...)
- M.2 is faster (M.2 does nothing say about the interface SATA or PCIe/NVM; NVM is slightly faster but SATA still is more flexible, since it is suported by any OS)

Basic questions:
- are you modifying your PC or is it a box, which you buy once and throw away when aged?
- which OS(es) are you planning to use?
- are you using the PC for streaming?
- are you using the PC for transcoding?

Quoting AiAustria:

Quote:
...
Partly disagree on:
- moving the Own Files/Pictures folders to the hard drive (especially with photo browsing this is annoying...)
...

This highly depends on the size of those folders. The intended SSD "only" has 256 GB, of which a quarter to half is easily used for windows 10, restore points and the necessary free space for W10 updates/upgrades. Then there is the size of all installed programs (Program files, AppData, ProgramData) and programs like Thunderbird and Outlook store their files also on C:. Mailboxes can grow very large... And Kahless wrote he's into very big files.
Also for privacy: depending on the problem with a PC, if on the SSD you won't have your private data files to yourself if the PC needs to be returned for repairs.

Quoting kahless:

Quote:
...
I'm a little bit concerned about 8GB RAM as I managed it to "kill" my current 16GB when copying bigger files from/to HDD or memory cards...

Using Task Manager you can see how much memory an application takes. Disk cache is "invisible" in W10, so what application are you using for file transfer? I do not see problems with File Manager.
Besides, disk throughput (solid state or otherwise) is always the bottleneck. Even on a USB3 solid state stick a lot of time is "lost" due to updating the disk directory after each file transfer. Easily seen if you copy a lot of small files in one go.

Using manual virtual machines can be a good reason to have more memory and CPU-power. But how much may 'fun' cost more?

Quoting kahless:

Quote:
- are you modifying your PC or is it a box, which you buy once and throw away when aged?
->in general no modifications planned as I buy what I need in advance

As of today maybe you should consider to add RAM later on, since currently the RAM costs more than 100,- € per 8GB, which is more than three times what it costed last year.

Quote:
- which OS(es) are you planning to use?
->Win10Pro

Then you are on the safe side concerning SSD compatibility. You don't have to worry about which SSD interface to use...

Quote:
- are you using the PC for streaming?
->Yes!

You should be aware, that not all CPU/graphics combinations are able to stream 4K. Not the only article about this very confusing issue, but the shortest: here

Quote:
- are you using the PC for transcoding?
->Nope, only converting CD to MP3

... then any quad core CPU should do it (hyperthreading or more cores won't generate any benefits, all current CPUs are capable of running hypervisors (VT) and the little difference in cache memories don't justify larger CPUs. You can safely ignore the base frequencies, as for desktop systems the single thread performance is the crucial part, which is expressed by the Max Turbo Frequency.

Quote:
- using Oracle VirtualBox-machines (just for fun)
...
I'm a little bit concerned about 8GB RAM as I managed it to "kill" my current 16GB when copying bigger files from/to HDD or memory cards...

Yes, virtual machines can really be a RAM issue. I'd definitly look for a system, which can be upgraded beyond 16GB. But as said above, today this is very expensive.

Overall, I'd check a business PC from a large manufacturer with a fast Core-i5 CPU (Kaby Lake i5-7600 or Coffee Lake i5-8600), 8GB RAM expandable to 32GB (without dumping the already purchased RAM - needs four sockets), which supports HDCP 2.2 and dual 4K@60Hz screens. Most business PCs already come with Windows Pro and many offer on site support for a reasonable amount of money. I won't worry about the technical aspects of the SSD, but about the size. I won't go lower than 500GB