Paragraph #2
ふだんから気軽に利用していると、だいたいの勝手もわかるので、いざ調べものや研究でもしようというときにあわてずに済む。
Let us make use of the commas for the purpose of parsing. "A, B, C." is the structure. Throughout the long sentence, the hidden subject is "one" or the generic "you".
A = Reason, B = Primary Result, and C = More Specific Result.
In A, と means "if". "If you use (the library) casually and regularly ----"
B = "you will get to know generally how things work (in the library)"
C = "and (as a result of B), you will save yourself from panicking when you need to do a research or study."
Paragraph #4
現実の問題としては、日常においては近所にある地域図書館を、少し専門的な問題については都心や県立の図書館を利用するという二段構えの作戦をとるのが能率的だろう。
Summary: Use two different libraries for two different purposes. The author calls this strategy 二段構えの作戦.
Use 地域図書館 for 日常 matters.
Use 都心や県立の図書館 for 少し専門的な問題.
"As a practical issue, it would be efficient to employ the two-step strategy of using a nearby community-type library for everyday matters and using a (larger) midtown or prefectural library for the more technical matters."