I know what 'von' and 'van' are about, but there's 'zu' and 'von und zu' as well. Why?

Germany and Austria
See also: German nobility, von, and Austrian nobility

In Germany and Austria, von or zu generally precedes the surname of a noble family, with a meaning identical to de in Spanish or French (in, for example, the names of Alexander von Humboldt and Gottfried Heinrich Graf zu Pappenheim).

As in Spain and France, not all noble families use a nobiliary particle. The most ancient nobility, the Uradel, are especially apt to omit its use

https://en.wikipedia.org/wiki/Nobility_particle

The word means "to" or "upon". So a name like "Viktor von Müller zu Aichholz" (a 19th-century figure) would translate as "Victor of Miller upon Aichholz" - the English equivalent is less common, but it would be like referring to Shakespeare in full as the Bard "of Stratford upon Avon".

But what about ones like Ernst zu Munster? Or Friedrich von und zu Gloggnitz? (OK, I made the last one up - but not Gloggnitz - as an example of a type.)

Found it. Von = of - where they came from. Zu = at - where they are. Von und zu = they came from there and they've still got it (rather less common...). So the fictional Friedrich von und zu Gloggnitz would be from a family enobled when they were in possession of a main estate in Gloggnitz - and which they still own. This is the theory - some probably just keep the particle as there's no official standing for nobility in Germany any more. https://en.wikipedia.org/wiki/German_nobility