Then the math to see what resistors I need--
5v supply - 3.3v consumed by the LED = ~1.7v left over
20 mA = 0.02A
1.7v/0.02A=85ohms of resistance needed according to Ohm's law
Looks like I need a 100ohm resistor which is the nearest single resistor I can use for each LED. (I could put resistors in series and add the resistances but that seems like it is unnecessarily complicating things). I can go as high as 15% on the tolerances as 100ohms-15%=85ohms but 10% or better would be safer.
Check my work via the conveniently available tools online:http://led.linear1.org/1led.wiz?VS=5;VF=3.3;ID=20
Then when I have everything assembled I'll put my meter on the tail end of things to see what value of resistor between the LEDs and the transistor should be or even if I need one. (I don't trust the numbers I've been given by the site I bought the LEDs from, but they are good enough to speculate on.)
And one 1K resistor between the Arduino and the transistor.
On the Linux side: so far it has just been adding the arduino package with apt-get.
I'll just be posting updates as they happen. From here on out, I think I have everything under control.