Hi Maxer,
As I said before, of course it won't work without having a reset button and a person to operate it, while watching the LEDs.
I'll try to find time to sketch a CD4017 circuit for you. It will work better if you disable the blinker and let the CD4017 just keep scanning as long as your turn-signal switch is on.
The CD4017 can supply about 10mA to each LED. If that is not enough current, buffer transistors are needed for more current (more brightness).
Since vision is logarithmic, there is very little difference in brightness between 10mA and 20mA.
Have you considered that your extremely bright LEDs may be that bright only because they are focused into a very narrow angle? Then they won't be seen very well from an angle. I would suggest using wide-angle LEDs for this application.
Why did you select white LEDs? Most turn signals that I've seen are red or amber. If you put a white LED behind a red lens then the light output will be very low because a white LED is a blue one with a yellow phosphor (no red). I don't know how much reduction in brightness an amber lens will cause, amber has some red in it too.
Lots to consider.