Just so you guys understand this, the X and the Z axis in blender and unreal are identical. It is only the Y that is in the opposite direction.
The way you can visualise this is to make a little finger pistol with your hand, with your thumb pointing up and your index finger at 90 degrees to your thumb pointing forward. Then put your middle finger at 90 degrees to both of those. So if you do this finger pistol with your left hand, you have the Unreal coordinate system, so get a Sharpie permanent marker and write a big U in the palm of your left hand. If you do it with your right hand, you have the blender coordinate system, so write a big B in your right hand. So your thumb is pointing in the positive Z direction, your index finger is pointing in the positive X direction and your middle finger is pointing in the positive Y direction. If you do a Tom Cruise double finger pistol, pointing your index fingers forward you can see the problem. Your middle fingers (Y axis) are pointing towards each other. Your thumbs are parallel, your index fingers are parallel, so no issue with X or Z No matter how you try to rotate your hands you are never going to get these three different axes to line up.
That all being said the advice to just leave it is probably good advice. I always export on the default settings of -Y forward and Z up when really it should be +X forward. It seems to work anyway. I think as long as Z is up, you can always rotate your mesh on the way in, using the Transform > Import rotation part of the FBX Import Options panel.
Just remember that you want your characters, your weapons and your vehicles to all be pointing in the positive X direction and you should be okay.