be practical, if u are driving individual leds (or a few leds per segment), you need 4 x 9 segment = 36 transistors, it is a lot to do on a breadboard. each transistor has 3 pin, each led 2 pins, each resistor 2 pins will need hundreds of tie-points and the fact that breadboard are connected column-wise (5 points per column), it will be difficult if impossible to lay them out properly.
switching from blue to red led is a wise move, u can drive them leds directly if eventually u want to do that. for blues, its not possible because of voltage being too low. get a few red leds and try laying