vtterp:
Does all of this sound right?
Yes...but bear in mind that some of your LEDs might only need 3.0V.
If you use the 'correct' resistor for 3.2V then the 3.0V LEDs might receive much more than 20mA. This is because a LED doesn't have a constant resistance. The resistance of a LED varies with the voltage across it and drops away exponentially as you approach the 'optimum' (in this case when you get 20mA). At 20mA a tiny error in voltage can produce a massive error in current, enough to hurt the LED.
To light up a LED safely you should either:
a) Use a circuit which controls current, not voltage (eg. A LED driver chip).
b) Aim for less than maximum current, eg. 15mA (the LED resistance curve is much flatter here so errors don't matter as much).
This page has more info: LEDs