I've moved your thread to the Magento 2 section as it was posted in the Magento 1 section.
Anyway as for the 75 external JavaScript requests, AFAIK when you merge the JS files it should only merge the JS files by Magento and it will not affect external JS files.
Can you list down the external JavaScript requests here?
Some external JS may be unnecessary or can be re-hosted but some of them are quite important and there may be no way to remove them (you may be able to defer them or prevent them from blocking the other elements from loading).