How can I make emacs open next directory in same window?

[ssecorp]

I have some things about emacs I find annoying.

1. If I have split emacs into 2 windows and in one I open a directory
in one and click on them it will open in the other window, how can I
make it open in the same window?

2. If I have solit first into 2 vertical windows and then split one of
them into 2 horizontal and I want to undo the last split, can I do
that? C-x-1 undoes all...

3. If I want to split into 3 equally big windows and not split into 2
then split one of them into 2, how would I do that?
I want 1/3,1/3,1/3 not 1/2,1/4,1/4