I had the character facing down problem too, I fixed it by unparenting the mesh from the armature, this will also fix having to use T0 as ref pose. Also, you should always export with scale set to 1 in the FBX exporter. You can scale up your objects in blender, ctrl+a and apply scale and your armatures will import with correct scaling. I like to use metres to get the right size when making objects and by default unreal uses 1 unit = 1cm, so in blenders scene tab I set the units to metric, and the scale to 0.01, and this makes 1cm in blender = 1 cm in unreal.