How can I decrease the maximum number of files where Get Info will open multiple windows?
At least for 10.7.5-10.9.5 the assumption that the number of Get Info windows is restricted to 35 is wrong.

Instead the screen resolution and the size of the Get Info window seem to be the restricting factors. Using a 1920x1200 px monitor I get 6 windows in a row and 12 rows (= 72 windows).

Trying to get the info on 73 objects and more a summarizing Get Info window will open.

Apparently there is no simple hidden numerical threshold of simultaneously opening Get Info windows.

To simply have an identical behavior for cmdI and altcmdI map cmdI to altcmdI for the Finder.app with a key remapping app.

If you don't want to use a remapping app use System Preferences -> Keyboard -> Shortcuts and create custom Finder shortcuts: Get Info -> shiftaltcmdI (to disable cmdI) or Get Info -> altcmdI and Show Inspector -> cmdI to swap the shortcuts of Get Info and Show Inspector. The same applies to Get Summary Info (with a different shortcut of course) if you prefer to change that one.



To quickly close all Get Info windows hit altcmdW or for some system versions alt-click on the close button of one of the windows. All other non-Get Info windows will also be closed though.