Well the central question is why did you raise the money? Your case seems to be atypical, but I think the best thing to do right now is to grow your business.

Instead of letting everything stay on a static basis of consistent 5k burn rate on a 9k monthly revenue, why not think of strategies to increase burn rate and increase revenue? If you took investor's money, I believe the key thing to do right now is to think how to increase your investor's stock value, which will also benefit you.

Don't even consider putting in a CD and Savings. If you do, it would be considered unethical if you're going to earn your investor the pathetic 3-4% in risk free asset, he's better off investing it from a mutual fund.

Hire. Spend. Grow. Never let cash sit idle, be a magician and transform money into more money.