Because Afrikaans does not capitalize all nouns.
Unlike German, ordinary nouns in Afrikaans are usually written in lower case unless they begin a sentence or are part of a proper name. So:
Only the first word, Die, is capitalized because it starts the sentence.
Yes, you can. That word order is possible in Afrikaans.
If you start with In die kombuis, then Afrikaans keeps the finite verb in second position, so you get:
This can sound more marked or slightly more focused on the location. The original sentence is the more neutral, straightforward version.
A rough English-friendly guide is:
dee mah-ri-NAA-duh is in dee kom-BUYS
A few notes:
If you want to sound more natural, getting die right is one of the most important first steps.