1) You have 99 LEDs. When they are all turned on, if they are fairly bright at 25mA each, then the total current is 2.5A!
2) You could use a 12V supply, and if the LEDs are 2V red ones, you could wire 5 in series with a current-limiting resistor. Then you would have 20 strings which would draw only 475mA when they are all on and bright, and they will all be at the same brightness.
3) Connect a small NPN transistor to each output of the 4017 as emitter-followers, then they will provide enough current for the many diodes.
4) Use the power transistors as common-emitter, with the strings of LEDs at their collectors. Then they won't heat because they will saturate when turned on.