Remember that bootstrap grid row is of 12 column, so what ever offset or column you are using it should add up to 12 and to target small screen devices such as mobile use col-xs-*. Everything else is fine.
If you want the same styling for small devices as well as large devices, you can omit the md styling and just use sm. If the width get's really small, you can remove the offset and use that gained width on the elements instead on xs widths.
To fix the buttons being cut off, remove the btn-block class.