Perhaps you're right; however, what about the settlement of Russians in, say, the Caucasus? Would that be a good analogy for this?
Which settlement? The 19th century settlement of the plains was enabled by the ethnic cleansing of the local tribes, Circassians and others, while the 20th century settlement was more urban-centered.
Yes, but one could likewise argue the reverse: Specifically that the high standard of living in these territories would encourage more, rather than less, Germans to settle there--specifically in urban and suburban areas there.
Why, if they're Czech urban and suburban areas where German is at best a minority language and at worst unpopular?
Let's say that Czechia is a German protectorate in this TL with the hope of eventually outright annexing Czechia into the German Reich.
How would this Germany react to Czech nationalist opposition?