In stress the need for bcomplex is higher than rda - but how much? by 50,70, 200 or more?

Don't get your: medical information from friends, tv or internet scams. Eat a healthy diet and you'll get more than enough vitamins. If you're concerned, try the cheapest generic once/day vitamin you can buy.

Increased needs: Under stress a human body is often more physiologic active and requires more calories/nutrients. But from the perspective of specific micronutrients like B vitamins, I don't know there there is any data to suggest how much more and if your really need to supplement extra to any significant degree beyond even a comprehensive multivitamin. Good luck.