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Nice build. I've been using the SparkFun ESP8266 for my solar projects. It includes a LiPo charge circuit that works without any programming. It's $2 cheaper that the Adafruit charger board but quite basic. https://www.sparkfun.com/products/13231
Nice comprehensive project. I would suggest skip the LCD and use the bluetooth. I really like http://appinventor.mit.edu/explore/ for doing Android apps and remote monitor temperature and voltage on other Arduino projects I've done. I've also sprouted plants by a window and used NeoPixels to supplement in the evenings. I'm not sure what spectrum I end up with but generally full R and less G and B. Sounds like I should go full B and half or less G
Pin 2 and 3 are TTL serial. I believe a standard RS232-C cable you can get for USB will damage the inputs. You really need a Arduino Uno to program since it already does the USB to TTL conversion plus the Arduino IDE has all the functions to load the bootloader and program the chip.