What about the verbs I used in this case and the tenses I chose?

- My mother would have been quite happy if I had taken care of the garden and watered her flowers, but while climbing down the steps of my house I tripped over and fell down to earth.

1) Are all the tenses correct?
2) Is "climbing down" the correct expression or I'd better use "going down"? What's the difference between them if there is one?
3) Could I substitute "tripped over" with "toppled over" or would this change the meaning?
4) "to fall down to earth" or "to fall down on the ground"? Any differences?