What is the impact on search engines if meta keywords has a very huge number of keywords?

Having the meta keyword tag also gives your competition a clear idea of what you're trying to optimize and rank for.

Yes, Google can see that as page is using keyword stuffing / spam technique and can hurt ranking. What do you mean "second keyword tag"? I see only one. If you place 2 of them, then Google would look just first one, but it considered keywords meta only in far past, now it don't consider it at all. But can be sign of spam site, so you can get only negative points, not positive for sure.

Now, search engines doesn't care about Meta Keywords tag, they don't even consider it. It won't benefit you but may get penalized for keyword stuffing.

Google has now stopped looking for meta keywords tag.But if still there are a large number of keywords ,google may consider it as keyword stuffing. But the other search engines like yahoo still consider meta keyword tag as a part of ranking.So choose your keywords wisely and in a limited number.

if Google is your target just don't use meta keywords. Google don't use it. But if you need tu use then 5 keywords is a good number, no less no more, and don't use 2 meta keywords, don't act as a spammer and you will be good