bikebikebike

Sorry if this is discussed elsewhere, but I have been looking long and hard and missed it, if it is.

I have several bikes and want to keep some Master Links on hand.
I have all kind of set ups from SS, IGH's, old 10spd, newer 27spd's, ebikes
(Ok, I can't say no. They needed homes.)
I have been burned getting the wrong size Masterlinks
(big PITA. Inconvenienced, to be precise. I prefer to have everything in hand before starting a job)

I often can't get ID on a chain from markings, to determine size (not length).
I know there are LOTS of different chain sizes, even within the basic groups.

My Questions:

1) How can you determine a chain's size by measurement , before starting?

2) Do the 3+ basic chain group sizes just need the 3 basic KMC masterlink/Masterlink,Spring Clip Type
sizes?

I don't mean to over complicate this, but there really isn't an easily accessible answer to this,
and rather than go buy a bunch of stuff, I am trying to know what I might need.
I don't expect any "oddball" sizes or brands, but would like to know if I am up against one.

Thanks

With appreciation