Software Serial Esp8266 Programming
Software serial will NOT work at 115200. The fastest that I have been able to use the Software Serial library, reliably, is 38400. There are other libraries (Neosoftware serial) that may go faster, but probably not 115200. Your choices are to lower the ESP baud rate or use hardware serial to talk to the ESP and software serial (through a USB to TTL converter) to talk to the PC for trouble shooting ( you need to switch around to program the Arduino). Another way is to program the ESP using the Arduino IDE and the instead of using the AT commands.
Esp8266 Web Server Examples
What are you doing? It may be possible to do the whole project with just the ESP. The processor on the ESP is much faster than most Arduinos and has more flash and SRAM.
The lack of pins can be overcome with external chips like I2C expanders and shift registers.
Software serial uses timer, be careful when you are using software serial. Timer is also used for WiFi communication section if you don’t give enough time to WiFi routines it will create problem of stack error or misbehavior.
It is better to use software serial only when you need two serial ports and also avoid use of software serial for data reception. Software serial can be implemented on any GPIO pin of ESP8266. For this you need SoftwareSerial Library for ESP.
To add library in Arduino IDE, Library path is different for ESP8266 C: Program Files Arduino portable packages esp8266 hardware esp8266 2.1.0 libraries Software serial library can be included in your program using below commands.