1800 is called as eighteen hundred or thousand eight hundred

1- Correct 2- Correct 3- Correct 4- "Plus points" isn't a phrase we use, but you could instead say "One of her strong points," "One of her positive traits," or "One of her positive characteristics." 5- Eighteen hundred, for the same reason that I stated in my comment above: the same rule applies to "hundred", "thousand", "million", "billion", and so on: when it is just a standalone word to express a vague number, as in "Hundreds of dollars", "Hundreds of thousands of people", "Millions of people", "Hundreds of millions of dollars", you use the plural form. But when you attach a specific number to it, it becomes singular. "A hundred." "A thousand." "One hundred." "Three hundred." "Four thousand five hundred." "Eighteen million." "Four billion." 6- Correct, assuming that you mean to be speaking in the present tense. This would be used when listing events one after another, and probably only when predicting events in the future: "The stock market crash sets off a recession. The recession sets off a huge march. Before we know it, the country is in chaos." Most of the time, however, you'll probably hear it in the past tense (when someone is talking about something that really happened, in the news, etc.) "The recession set off huge marches around the country."