The LEDs can be placed in series with a single resistor. We use 80 white LEDs in series with a resistor for 240v. Use 4 strings and 4 resistors. No other parts.
for a constant current of 100mA I won't use an LM317L since it can supply just 100mA.
An LM317T can supply a constant current up to 1.5A.
Supposing your calculation is correct you won't even have to use a heatsink when choosing an LM317T instead of an LM317L.
With a power supply of 32V/1.5A you have a lot of freedom to play with different LED strings.
Just keep in mind not to exceed a total forward voltage of +Vin(-3V)=Vf(LED)Xn+Vreserve
where +Vin is the supply voltage ,
Vf(LED) is LED forward voltage and
n is the number of LEDs in a chain and
Vreserve is excessive voltage (over the voltage demand of one chain)
E.g. +Vin=32V, Vf(LED)=3.5V: (32V-3V)=(3.5V*8)+1.0V
Math is not my favorite stuff. All you need is to calculate for the maximum number of LEDs in a chain to have a little leftover of voltage (Vreserve, in that case 1.0V).
Given the max 100mA for the LM317L I will probably set them at 98mA, the difference is not noticeable.
My main issue is to use a resistor for each LM317, or if one single resistor can set the current for a number of LM317s. Also the one capacitor for the hole setup or one capacitor per installed LM317...
If you plan to control them with Arduino, you don't really need LM317s. In the example below, I assumed the Arduino is running at 5V. Use one circuit for each string. If your Arduino is running on 3.3V, change R1 to 680 ohms. I have not tried this on the bench, it may require 18R for 100mA.
(Note: Some sharp eyes will notice that I'm using a gain of much more than 10. That's because the transistor isn't saturated.)