Basically yes, option 1 needs to be soldered, option 2 is ready to use and can be supplied with power via a usb charger.
If you don’t want to flash it with alternative firmware you can go the Arduino IDE way and need to program everything in LUA (including MQTT support).
In my opinion it is easier to reflash with Tasmota (good support in this forum) or ESPEasy (also some support here, and has a nice web interface for configuration).
Nope, it can not be put on an ESP. You need a computer supporting java:
A lot of people are using a RPi as their openHAB server.
Yes. You need to define items for your MQTT setup and with those items and correct tagging you can use Google Home.