Rational and logical are quite similar in meaning but rational is something that has logic. These two words are close synonyms and not antonyms.
The author want the reader to feel terror while reading "The Cask of Amontillado"
I don't exactly get what you are saying, so I'm practically guessing. If you restate I will gladly help you.
It indicates that Huck frequents places perhaps grocery stores where the conditions are not sanitary what with "sickly eggs and rotten cabbages and dead cats" in other words, Huck cannot afford to frequent fancier shops or fancier homes because he is poverty stricken and used to such sights.
