You will find the explanation of “ποταμὸς Κύδνος ὄνομα” on page 142 where Mastronade explains the uses of the accusative case.
"d. Accusative of respect or specification. The accusative case is used to express the thing in respect to which an adjective or verb phrase denoting a state is applicable.
οἱ Ἀθηναῖοι διαφέρουσι τὴν σοφίαν. The Athenians excel in cleverness.
πόδας ὠκύς swift in respect to the feet, swift-footed
ποταμὸς Κύδνος ὄνομα a river Kydnos by name. "
I suggest that you read this section again. It will take some time for you to fully understand what M. says about the accusative case. Don’t rush it.
You should also drop the habit of trying to reconstruct the Greek by looking at the English. The two languages express the same idea in different ways. Just because idiomatic English requires “by” doesn’t mean automatically that you are looking for a dative in Greek. To understand the Greek as fully as you can explain to yourself what parts of speech are being used and give a reason. After a while this process will become more automatic. Translation is a goal not an intermediate step in understanding the Greek. Only translate when you fully understand the Greek.
As for μέν…δέ Greek sees an antithesis where it would be abnormal in English. Your goal should be to translate into good idiomatic English not to demonstrate that you understand every Greek word. Be aware of the antithesis in Greek but don’t translate it by the formula on the one had etc. It is very rarely correct to translate it like that. See M. page 100 :
“d. X μέν . . . Y δέ. A very important use of δέ, and one that is especially characteristic of Greek thought and idiom, is its use in combination with a preceding postpositive particle μέν to create a contrast between antithetic elements (or sometimes simply an emphatic link between enumerated elements). The force of μέν is to anticipate an antithesis by marking its beginning; the second element is most often joined by δέ. The contrasted elements may be single words, parallel phrases, or entire clauses. A common but clumsy English translation of μὲν . . . δέ is on the one hand . . . on the other hand; often it is more idiomatic to convey the antithesis by emphasis in pronunciation or by turning one of the paired clauses into an English subordinate clause introduced by while or whereas.
ὁ μὲν στρατηγὸς ἀποθνῄσκει, οἱ δὲ στρατιῶται φεύγουσιν. The general is dying, but the soldiers are fleeing.
οἱ μὲν Ἀθηναῖοι πείθονται τοῖς νόμοις, οἱ δὲ βάρβαροι τῷ δεσπότῃ. The Athenians obey their laws, whereas the Persians obey their master.
Note the position of the postpositives in these sentences: words like τε, μέν, and δέ often intervene between an article and its noun or between a preposition and its object; less commonly, the postpositive may be placed after the phrase unit: for instance, after an article-noun unit.”
No it doesn’t. Again you are trying to work the Greek out from an English translation.
In sentence 6. you have “τὸν ἄνδρα” as the object of “εὑρίσκουσιν”. “ἀπάγειν” is the complement of “ἐπεθύμουν”. As it is clear that the object of “ἀπάγειν ἐπεθύμουν” is also “τὸν ἄνδρα” it is not necessary to use a pronoun. This especially so because of the καὶ linking both parts of the sentence. As the sentence continues the object of “φυλάττουσι” is expressed but again not in the second part.
