GI? is possible to make realistic, internal and external scenes with photographic realism?
There is baked GI with lightmass and Light Propagation Volumes, which is a beta feature. Enlighten is starting to support UE4, but I’m pretty sure it’ll be a separate license.
area lights? what type: cylinder? custom objects? with .ies? with GI?
Only spheres and tube lights are supported with Lightmass (baked lighting). .ies is supported and works well. Light Propagation Volumes is implemented into the engine as a beta feature, not sure what is supported.
save render static scenes? rendering animation?
I’m not sure exactly what you are asking. You can capture images and video with UE4.
is possible to use HDRI images made in external programs? which format: .hdr? .exr?
Yes, .hdr is supported, I don’t think .exr is.