Electronic – arduino – Does the resistor value on D+ and D- line matter on Arduinos

It's similar to an arduino but with the USB to UART converter chip removed to be cheaper. In order to program it you have to use an external converter and connect it to the Rx/Tx pins.
Please note that these boards don't use a crystal as a clock source but a 16MHz resonator which has higher tolerance (0.5%)

You'll need to get an external USB to serial board (or cable), like

Note that there are two "versions" of USB to serial boards. One version outputs Tx pin to Tx header and Rx pin to Rx header and the other version outputs Tx pin to Rx header and Rx pin to Tx header.

If your board outputs Tx pin to Rx header and Rx pin to Tx header (the signals are already crossed) then you should connect Rx of the USB board to Rx of Arduino, and Tx of the USB board to Tx of Arduino (like shown below)

If your board outputs Tx pin to Tx header and Rx pin to Rx header then you should connect Rx of the USB board to Tx of Arduino, and Tx of the USB board to Tx of Arduino (cross connect like shown below)

As with many things, but unusually obvious here, calculus comes to the rescue. Your senstitivity is $$ \frac{\partial V_{out}}{\partial R_{LDR} } $$ You need to find the expression for $$ \frac{\partial^2 V_{out}}{\partial R_{LDR} \partial R_1} $$ as a function of the resistance of the LDR and R1, set that equal to zero, and find the value of R1 when that derivative is zero.

Formally, you should take the second derivative and make sure its a maximum and not a minimum, and test your endpoints for absolutes, but in this case I'm reasonably sure that won't be necessary.

My gut feels like R1 should be 400 ohms, but my gut's been wrong before and will be again. (@Wouter-van-ooijen seems to think it will be an absolute at one of the endpoints. Interested to see what the right answer is)

Note that this in no way spreads your range of Vout over the dynamic range of your ADC. You may well need to do some signal conditioning beyond that circuit.

Oops, just noticed that the LDRS aren't 100 ohms like in the picture. The answer should be that R1 should be set at the total value of the four LDRs, which is right in line with Wouter. This will interfere with the adc, and you should buffer.