1.There's no need to say 'in'. You can say 'I'm home'. It is also correct to use "at" like this 'I'm sitting at home' or something like that. 2. Yes it is. 3.When there's a be verb (am, is, are) in your sentence, yes/no questions are made using be. When there's a main verb (speak, go, study....) you should use do/does. In order not to get confused, try to think of a sentence first, then turn it into a question. 4. The right sentence is " I've never seen it before." which is present perfect. 5. Imagine that you want to go somewhere and you want to ask if a friend would like to join you. It's definitely a common question to ask.