Creating a new folder with Diablo is a waste of time, effort and storage. You only need one installation to run multiple copies. I will explain below, but first, lets take care of your 64bit issue...
The game is set to run in 64bit mode by default. There is a toggle in the game for 32-bit.
However, if you look inside of your Diablo folder, you will notice that there is a launcher and a Diablo III.exe in the root folder just as there always has been. There is a new folder in there called x64. This contains the 64bit version of the game. If to follow the instructions below using the Diablo III.exe from the root folder, you will have no issues:
Let's get you a new shortcut on the desktop to open as many copies as you need from one installation:
Go to your Diablo III folder where the game is installed.
Find the BLUE icon in the Diablo Folder.
It is the one called Diablo III.exe
Right click on it. Create Shortcut.
Move the shortcut to the desktop.
Right click on the shortcut that is now on your desktop, go to Properties.
Find the TARGET: box.
Add these spaces and items to the end of the line:
"C:\Program Files (x86)\Diablo III\Diablo III.exe" -w -launch
***Leave the quotes where they are, just add a space after the quote, then -w, then another space, then -launch.
Click "Apply" or "OK" and close the properties window.
Now you should be able to double-click the shortcut as many times as you like to open as many game copies as you want from a single installation.
