How many user accounts should you have for yourself on your Macbook?

I understand your intentions by following the Principle of Least Privilege that is taught in most IT and Computer Science courses. The theory being that if someone gained access to a standard users password, they would not be able to change higher level administrator settings. This does work in a business environment where you do have an IT department for Admin tasks and you do not want standard users to mess up settings on the device that only the Admin should change and usually involve multiple networked computers. I see this as more of a protection from letting employees screw up settings that would have a negative impact on the network, than from preventing an outside hack.

Using a Mac as a single user I recommend sticking with the single Admin user. There really is not even a need for a second backup admin account.

There is no benefit to having more than one User Account. If you want to create more, that's perfectly ok.

... create an additional account with the standard role to separate normal daily work from rare critical administration tasks.

The practical effect of creating a separate "standard" Account lacking Admin privileges is that there will be such a frequent need to provide your Admin Account credentials that you are likely to become inured to providing them to the point of complacency. At the very least it will be annoying. But if that's what you want to do, fine.

Regarding Apple ID account security: Security and your Apple ID - Apple Support. An Apple ID account is obviously separate from a Mac's User Account. You can have as many of them as you please also, but just like a Mac User Account having more than one will just complicate matters. Make sure that each family member has a unique Apple ID - Apple Support has more on that subject.

Both of you can have Admin accounts, assuming of course you trust one another to make changes to that Mac. Otherwise decide who wants the responsibility for maintaining it, and relegate the other Account to Standard.

You can each use your own Apple IDs as well, although certain features (such as Find My) may only be linked to one Apple ID. The idea is that a Mac should have only one owner, despite the fact multiple people may be authorized to use and administer it. Should you attempt to make conflicting changes macOS will inform you.

If you have even the slightest concern about the possibility of one User Account becoming corrupted, that would imply you don't have a contingency plan for that. It goes without saying if you care about the information on your Mac, use Time Machine: Back up your files with Time Machine on Mac - Apple Support. The converse is also true — if you don't use Time Machine then the prospect of spontaneously and irretrievably losing all the information on your Mac does not concern you. Not everyone does.

If you should even encounter a circumstance in which you suspect something amiss with a User Account just create another temporary one for the purposes of testing, as Apple suggests in Use safe mode on your Mac - Apple Support when discussing the effect of Login Items.

Would I in this case be able to correctly configure the hardware and all kinds of external software correctly for those 2 standard users with my admin user account, although the admin is unrelated to both standard user Apple ID’s?

Yes.

What if for example, there is a software I would need to install as the admin user, which both standard users need to use, but they need to connect the software each to their personal AppleID (save configuration on iCloud from within the software or something like that)? Do these sort of things happen and would it be a suitable way to handle it (so general installation on laptop from admin user, individual configuration independently for each standard user)?

Yes. They can do that. Each user will have his or her own documents, preferences, apps (unless you want to approve them for all users), app settings... etc and be responsible for maintaining them. If they should make a mistake none of its effects will propagate to other users.

In your role as that Mac's Administrator, you will have an occasional need to approve actions with the potential for altering various settings and options. In other words you will become the "IT department" with all rights and privileges pertaining thereto 🙂

Minimum two admin ... one primary and one standby for when the primary gets corrupted.