When you're doing the macro coupler thing, it doesn't really matter if one lens was macro or not before you started - the combo will be macro (and macro only).
The new, 'real', focal length - I have no idea, lol! I just know how to figure out the magnification factor.
Working distance will be VERY short - only a few inches (if that) from the rear element of the reversed lens. Tripod is 100% required. It helps if you set it up so that the lenses are pointing straight down.
It's easier to focus by moving the subject. You'll have to shim it up and down with books or whatever you can find to get it in the 'focus zone'. You'll have to focus manually, and nearest focus to infinity will only be a few millimeters. It's a painstakingly slow process, but once you get everything dialed in - you'll have more macro than you know what to do with.
Timer, mirror lock-up, remote - all of that. Do everything you can to minimize vibration.