Is “much” plural?

Yes, that's right. "Much" takes the singular verb. Compare this with "many," that takes the plural verb.

"Much has been written about the controversy between religion and science." (Much writing)

"Many have written about the controversy between religion and science." (Many writers)

Much is not exclusively plural. Let's imagine you are shopping and a salesperson shows you three styles of shoes. You ask them, "How much are they?". By so doing you are asking the individual prices of the three seperate shoes or the three collectively. Only you know what you mean.

This one is $50.

The blue one is $45.

This leather is the most expensive. It is $65.

However if you are refering to the examples above the latter is correct. Sorry.........

Um, "shoes" is still plural.

If you're looking at a batch of widgets, though, and you ask "How much are they," it's simply idiomatic, as well as ambiguous. The merchant could respond, "One hundred dollars," and you wouldn't know whether he was talking about one, a set, or the whole batch. In real life you'll instead hear things like "Fifty dollars a dozen," or "Ten dollars apiece," or "I'll sell the whole lot to you for a hundred dollars."

Oh, and I'm not saying that "much" IS a singular word, nor am I saying that "many" IS a plural word. That's just the form of the verb that goes with them when they're used with an understood noun following.

(cold in the head, fair warning, I may not understand this next time I look at it. Phoo.)

please