Improve file-info visibility in Finder's preview pane
Sadly, I don't think there is the level of customization in the Finder that you want. 

There are "Finder alternatives", like Path Finder, which may lay out information in a better way.

The default size of a Finder window can be set as follows:
1. Close all windows.
2. Open a window and make it the size you want.
3. Close it. Now all new windows will be the same size.  

(Since Classic MacOS days!)