Really? Can you provide an answer for any of these answered by philosophy? On the contrary, it is the sciences that provide answers to these questions, to the extent they are meaningful or the answers are known.
Philosophy is a science. Aristotle answered the essence of theses questions 2400 years ago. He may have commit some mistakes, but the essence is there.
For the question "How does one acquire knowledge?", I recommend Kant, Hume, Russell, Carnap, and Popper, for a start.
I'd like to ask you how you find out if a question is meaningful? And please don't answer "if it can be answered by science", because then you have a circular argument.