Elaine, congratulations! You have navigated the pronoun landmines with great agility. Each of your sentences uses commas correctly, even though there are different reasons for each sentence. In the first there is no reason for commas at all. In the second, you have an introductory phrase set off by a comma. In the third, you separate an unnecessary word (however) by commas; and, in the fourth, you use a comma as a conjunction between two clauses. Do you want to sign on as my assistant?