I'm planning on building an LED circuit to place inside a model miniature for wargaming. The circuit would be in parallel as I'd need a really big battery to power up all the LEDs.

I wanted to check my understanding of setting up the resistors so things work properly. I'm going to have different types of LEDs with different voltages but here's my basic question.

Let's say I have 10 blue lights at 3.4V 20mA and a 9V supply. Based on my calculations each lamp would need a resistor of only 28 ohms? My math is

\$\frac{9-3.4}{\frac{10\cdot 20}{1000}} = 28\$

Is that right? The final circuit will have close to 20 LEDs, and it seems like at that point the ohms of the resistors will get much smaller?

Once I figure out all the different types of lights (all at 20mA), I will need to calculate the resistors individually for each as they have different voltage requirements?