Is it essential to re-invest all the revenue back to the business?

That's a pretty big question!

Depends on how much money you're making and how much you can usefully spend. No point spending for the sake of spending, but if you believe spending will yield an increase in revenue, and you'll get more back than you spend, then certainly.

You might also want to consider the tax structure of your jurisdiction, such as whether there are some kind of tax credits for R&D spend, and whether you'll be punished (taxed) for making a profit. No need to give away your hard-earned to the Evil Agents of the State if you can avoid doing so by sensibly investing it back in the business.

As to how... again, a big question. If you're not getting enough traffic then that might suggest you're underspending on marketing. On the other hand, if you're getting traffic but not converting to sales, then you could do with knowing why - maybe your product lacks features that people are looking for, and need to spend on development.

And well done on having revenue!! That's the hard part!

IMO it depends of whether you're aiming to build a lifestyle business or a traditional high growth startup.

If you have revenue enough to sustain the lifestyle you wanted from it, you'll probably choose to maintain that level and enjoy the spoils. You will, however, be vulnerable to competitors and your business might become less profitable as time goes by.

There's no sustainable passive income, remember. You might be able to alternate between months of reinvesting and months of enjoying what you've built, but if you only take from the business it will eventually dry out.

On the other hand, if your goal is building a high growth startup, you'll need to invest as much time and money into it as you can. Every dollar you take for yourself is 100 dollars you'll lose down the road. Of course you'll also be vulnerable to competitors and to your own mistakes hindering the growth of your business and you simply wasting the money you invest on it.

As to how to use your revenue:

• Pay for freelance writers or designers to fuel your content strategy;
• Advertise on Adwords, Facebook, Instagram and Reddit and test the ROI;
• If you have enough to start hiring, hire people good at what you don't do well (i.e. if you're a developer, don't hire another developer, hire a sales person or designer or whatever your biggest shortcoming is);

Beyond that, only you can answer the question I believe.

Hope that helps!

I would use part of it for advertising your product.

You could just put it up against any other traditional Investment. After all your life needs are met. How much ROI do you get for each $1 within your company and how much If you take it Out and put it into a Fund, a Stock or somewhere else...