Q1: The "over" implies that you have your friends at your house or apartment rather than out at a restaurant or a public setting. Q2: "Back home" isn't needed if you just want to say you send letters to your family. "Back home" is usually used when you are away either at college or in a foreign country, but you don't need it to complete the sentence. Everyone will know what you are talking about. Q3: Words like "though" are filler words that we use to transition between sentences. In this sentence, "though" is being used to reference the previously sentence. Based on the context, I guessing the person is using it to mean "already," but its hard to tell exactly without the previous sentence. I'll show you an example to try and explain it better. Person 1: You should buy a new bag if you can't find one. Person 2: I know I have a bag though. Person 2 is using though in reference to person 1 telling them to buy a new bag. It isn't needed. Person 2 could simply say "I know I have a bag" and it would be the same sentence, but adding "though" is a different way to say it.