The sentence could have been written as follows: "These flowers are beautiful." Because flowers is plural we use "these" and if there were only one flower, we would say "This is a beautiful flower." These is the plural form of this, just like "those" is the plural of "that". The word "what", at the beginning of the sentence adds emphasis to the statement and is referred to as an exclamation (excited statement), e.g., What a great day! / What a silly boy!. The exclamation "what" usually followed by an article, then an adjective, then a noun, e.g., What a beautiful flower! But if the noun is plural, we do not include the article, e.g., What beautiful flowers.

Yes, it's right. Since the emphasis is on 'these', the flowers have probably been found after searching among a bunch of other flowers.