Step 1: Understand the context of the sentence.
The sentence refers to Hastings, a seaside town, developing into a holiday resort after World War I. Hence, the correct sentence structure and capitalization are essential.
Step 2: Evaluate each option.
Option (A): Incorrect, "the first world war" should be capitalized as "the First World War."
Option (B): Correct, the comma before "a seaside town" is appropriate, and "the First World War" is correctly capitalized.
Option (C): Incorrect, "Town" should not be capitalized.
Option (D): Incorrect, "A seaside town" should not have the article "A" in this context.
Hence, the correct answer is (B).