Sprang is to leave something/someone with a quick movement and strand is to leave Some one/something with out leaving your desired spot like if you were to break up with someone you left them by their self "stranded"
The character trait reveals about della that she feels it is important to dress with modesty.
The Cunninghams maybe the poorest family in Maycomb but they have a certain principle to follow. For instance, they do not accept anything if they can not pay it back. They repay the people they owe by exchanging crops and chopped woods from their farm.
The adjectives are strong and close