"There are a lot of men."
Both readings seem to be valid. タイ勢 uses the original (Chinese) reading of 大 and seems to be used most frequently to mean a general trend or situation, “zeitgeist”.
AFAIK Duolingo doesn't provide a way to attach different readings per every exercise to each tile. That's why most kanji sound in kunyomi even when they're going to be used in compound words.
Wrong in the given context is what I should have clarified. I'm aware of various readings, however it specifically changed from the correct reading to the wrong (in this context) one since the change of TTS voices. The course contributors, as far as I am aware, can't do anything about some Kanji-combinations giving out 'wrong' pronunciations, unless they force them by writing the word in Hiragana. Until the TTS gets a way to work around this issue, there's not much we can expect here.
If you mean an answer by actual "duo devs", no, this is a community forum. There are mods and the course contributors, but if you have any technical issues you're better off writing to the official support. Any language questions are asked here, with other community members answering. Always consider checking other sources as well.
Duolingo Plus only gives you unlimited hearts (where available), the option to download lessons for offline use and ad-free learning, plus you obviously support development with money.
It's better to use 男の人 than 男alone, the latter is less formal, more like "fellow, guy, chap, bloke".
In 男の人 the noun works as a prefix meaning "male", so it's "male person" or "man" of course.
If you absolutely want to use the more casual version you'd have to change the sentence ending as well, like so: 「大勢の男がいる。」, because mixing politeness levels sounds awkward and not natural.
No... those are two different verbs for different purposes (and some shared uses). います/いる is the existence (to be) verb for animate objects (people, animals etc). です/だ is a copula meaning "this is that/A is B" as in AはBです。For example, 私は犬です (I am a dog) or leaving off the subject/topic, 犬です (It is a dog) where "it" is from context. But 犬がいます would be "There is a dog". See, in English we use "to be/is/am etc" for both purposes - to show equivalency (です) and to show existence (います/あります) but if you think about the example sentences you'll see there's a big difference between saying "It is a plant" and "There is a plant". I hope that helps!
I should add that there is more to it than that. です is sometimes added on to the end of a sentence just to make it polite (and other reasons). That can be confusing when you've learned its translation as "It is ___".
A lot of adjectives in Japanese act just like verbs, and are conjugated as verbs. You can simply end the sentence with them for the reason that a Japanese adjective's meaning is "it is ___"; for example "おいしい" by itself means "it is delicious". So, you can say "寿司はおいしい！(すしはおいしい！) The sushi is tasty!" or if you're being polite, "お寿司はおいしいです！" The sushi is tasty!". The meaning is the same. So just try to remember when you see a sentence ending in an adjective like おいしい or 難しい etc, the です that follows (if there is one) is just ornamental.