Android Development: building my app to fit different types of smartphone
===

My app consists off buttons on a screen with some text. Its really simple as that's all it needs to be.

But when I test my app in different virtual phones it looks different. Now as I'm not using images I'm assuming that as long as my images are in the drawable folder and not all accommodated in different drawable-**** folders that they won't be an issue.

But how do I code the XML to fit all SMARTPHONE screens. 

XML: 

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/textView1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:padding="@dimen/padding_medium"
            android:text="@string/welsh_libs"
            android:textColor="#FF0066"
            android:textSize="30dip"
            android:textStyle="bold"
            tools:context=".WelshLibraries" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <Button
            android:id="@+id/button2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#6088A1"
            android:textColor="#FFFFFF"
            android:text="@string/news" />
     
     	<Button
            android:id="@+id/button3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#50C0E9"
            android:textColor="#000000"
            android:text="@string/find_lib" />

        <Button
            android:id="@+id/button4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#6088A1"
            android:textColor="#FFFFFF"
            android:text="@string/free_res" />

        <Button
            android:id="@+id/button5"
            android:layout_width="285dp"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#50C0E9"
            android:text="@string/ask_lib"
            android:textColor="#000000" />
        
        <Button
            android:id="@+id/button6"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#6088A1"
            android:text="@string/find_book"
            android:textColor="#FFFFFF" />
        
        <Button
            android:id="@+id/button7"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#50C0E9"
            android:text="@string/register"
            android:textColor="#000000" />
        
        <Button
            android:id="@+id/button8"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="18dp"
            android:background="#6088A1"
            android:text="@string/login"
            android:textColor="#FFFFFF" />

    </LinearLayout>

    <ImageView
        android:id="@+id/image1"
        android:layout_width="190dp"
        android:layout_height="0dip"
        android:layout_marginBottom="5dp"
        android:layout_marginLeft="70dp"
        android:layout_weight="1"
        android:contentDescription="@string/desc"
        android:src="@drawable/waglogo"
        android:visibility="visible" />
  
</LinearLayout>

I'm using dp's as the measurement unit but I understand to be the only units possible to use so I know its not like designing a website with pxs, ems and %s available.

Any help or links people can provide would be much appreciated.
Thanks,
Dan

P.S. I'm also looking for a way to scroll down if I want to add more buttons below the 8 present when the app loads. Any ideas?