Can I use it also for Android?

It is possible when you add some wifi module like ESP8266 or MT7681, and through the communication between serial and wifi you can control Turtle, and you need to have an APP which is support the wifi communication.

Is it possible to add some sensors in the microcontroller? I mean: are there some input/output ports available to be used?

Is it possible to combien this kit with a raspberry pi ?