"The ancient customs are very many."
Translation:Mores antiqui sunt plurimi.
also plurimi mores antiqui sunt was not accepted. If Latin is like Russian (also word order does not matter and lots of cases), when you put a word at the beginning it adds stress to it, so it sounds like you are saying "oh so very many customs" as if you're just in awe about how many customs there are, whereas the other way it sounds like you are just making a factual statement about customs.
I don't think so. We cannot consider that all superlatives have to be at the beginning of the sentence. A search through texts show it is not the case.
Even if the superlative is a particular kind of emphasis (in one extend, it's not a real one), it's not the same emphasis than moving a word, as Suzanne explained it very well.