幸好我下周将会工作五天。 Why luckily?

幸好我下星期只工作五天。个人觉得这句话用口语化更强的幸好更好。

幸运是下个星期我只需要工作五天

真幸运，我下个星期将会工作5天。 or 幸好，我下个星期将会工作五天。 Lucky always translate into 幸运 ，consider the context，真幸运and幸好 are both ok.

I think maybe you mean you are a poor student, who needs money. You have a part-time job. Next week your timetable allows you to work 5 days instead of only 1 or 2. (Just a guess.) 我很开心，下周可以工作5天。