Combining image and text within a button in kivy

Regarding to question #2.

The way Kivy works is embedding Widget instances. Since Image and Button are subclasses of Widget, then all you have to do is embed an Image inside a the Button. Notice that the positioning inside a widget is fixed. You have to give explicit coordinates.

That said, you can always embed a Layout to organize the stuff you are putting inside the Button.

Here is the simple ex

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder

Builder.load_string("""
<ButtonsApp>:
    orientation: "vertical"
    Button:
        text: "B1"
        Image:
            source: 'kivy.png'
            y: self.parent.y + self.parent.height - 200
            x: self.parent.x
    Label:
        text: "A label"
""")

class ButtonsApp(App, BoxLayout):
    def build(self):
        return self

if __name__ == "__main__":
    ButtonsApp().run()

EDIT: An example of how a relative layout can be embedded inside a button

In this case I am using a StackLayout to organize an Image and a Label inside. As I said, Button is a Widget and Kivy works embedding widgets inside widgets. It doesn't matter if they are labels, buttons or layouts.

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder

Builder.load_string("""
<ButtonsApp>:
    orientation: "vertical"
    Button:
        StackLayout:
            pos: self.parent.pos
            size: self.parent.size
            orientation: 'lr-tb'
            Image:
                source: 'kivy.png'
                size_hint_x: None
                width: 74
            Label:
                size_hint_x: None
                width: 100
                text: "The text"
    Label:
        text: "A label"
""")

class ButtonsApp(App, BoxLayout):
    def build(self):
        return self

if __name__ == "__main__":
    ButtonsApp().run()