Any best practices for positioning the Add Contact button (1) in this screen?
Left or Right?
The emerging conventional location for buttons like this is the top right (where your search box is) but that assumes that the action isn't a primary one.
I've suggested in this answer to a similar questions about list view switching, that this is likely due to the top right being a secondary focus area (or tertiary, depending on which scanning model you subscribe to. See the example of the Gutenberg Diagram below).
So if adding a contact isn't the main reason users are seeing this screen, then the conventional practice is to put it in top right.
If adding contacts is what this UI is for, it's reasonable to leave it where it is.
I would put it just right of the "Total" indicator (or perhaps just right of the "Back" and "Next" links that will appear there).
Same height and rounded corners as Search box, dark background color complementary to the table header. On narrow screens, search box could appear below the row with Total info and the Add button, but no reason to waste precious vertical space if the primary purpose is to display data..
Also a plain "plus in a circle" icon might be preferable to the current one "plus in a circle on a document, so small that it's hardly visible".
And as always, don't forget to test with volunteers.