Serge, the answers to your question are not as easy as saying this percentage or that percentage. The answers lie within the type of industry environment your are competing against and what the typical profit margins are.
What type of product are your selling (ie luxury item or common product)? What is your cost of product and markup? What is the market environment (high volume / low profit or low volume / high profit)? What is your market strategy and how much of the market share do you want? Does your product require significant re-investment and why? All these issues impact your decisions regarding profit margins and reinvestment.
About the only thing you can directly control is your cost. Focus your efforts on cost of product to manage your profitability.
Many governments keep industry statistics - this maybe a source of information for you. If you know of some competitors, try to get some information from them (you may have to use covert but legal methods). Good luck.