I'd happily say 'be careful climbing the tree'. I don't see that 'in'adds anything there.
In regard to deciding where to settle, there are various factors....
There are various factors in regard to deciding where to settle...
However, transportation may be so overcrowded and expensive that, in regard to deciding where to settle,
To me it sounds and feels better at the beginning. In the middle it seems a bit unnecessarily bulky and can be shorter and more direct. At the beginning, it can be used to help shape the focus, but once the focus has been shaped, then I would go for the shorter form.
By the third example, the sentnce is becoming a bit ponderous.