Ok, sounds lightmaps is the best way to go for you - i have little doubts about this. I don't see a need for a completely dynamic solution like voxel cone tracing.
I lack good experience on baking and uv unwarp with applications like Blender, but i would try this first to save a lot of time.
The primary issue is, to support normal mapping (if necessary) your light map texels need directional information, encoded in something like primary light direction, or spherical harmonics (2 band SH is mathematically the same as primary direction: 3 values for direction and a 4th for constant ambient, so easy to understand and good enough), or spherical gaussians etc.
You might wanna open a new topic and ask if / how Blender can generate this directional data, or if someone knows an application the can.
If you can't find a practical solution and need to bake yourself, MJP has good blog about it: https://mynameismjp.wordpress.com/2016/10/09/new-blog-series-lightmap-baking-and-spherical-gaussians/ and he also has a nice baking project on github. It's c++, but you might be able to use it (if allowed). There should be others as well. Beside Optix there is Embree and Mitsuba for ray tracing. All C++ of course, but maybe there are C# wrappers around.
For automated UVs i know those two: https://github.com/Microsoft/UVAtlas/wiki/UVAtlas (Halo) and https://github.com/Thekla/thekla_atlas (from The Witness)
For dynamic objects like characters a dense grid of low frequency probes seems the easiest approach, using SH2, SH3 or SG. (Low res cube maps would also work, but that's probably slower.) This is another point where i'm unsure if blender can generate this easily, but you could add small cubes to the scene (not casting shadows or contributing to GI), attach textures to each side, and turn the resulting lightmaps into SH or whatever afterwards yourself. I've learned about SH from here: http://www.paulsprojects.net/opengl/sh/sh.html UE4s advanced approach if this: https://docs.unrealengine.com/en-us/Engine/Rendering/LightingAndShadows/VolumetricLightmaps
Just some spotlights and ambient as you suggest might work, but the more photorealistic / consistent with the background you want to be, the harder it becomes.
For reflections (if necessary) a sparse grid or manual placement of probes is state of the art, missing occlusion for reflections is probably the most obvious problem we have with current graphics, but it should be acceptable.
From all this you should be able to get something comparable to the typical UE4 look using baked lighting, so high quality. (But remember how good the Witness looks even without normal maps - it uses only simple high res light maps)
56 minutes ago, evelyn4you said:- lights have static position but with slow day and night cycle. ( At the sunset sitting on terrace .. )
Sounds dynamic time of day is not super important and you might be able to use a changing enviroment probe or even blending between 2 or 3 light maps.
Otherwise this is an indication to precalculate just light transport and update final lighting at runtime, like Enlighten does. Good article here: http://copypastepixel.blogspot.co.at/ Those ideas are compatible with both lightmaps and probes, but i don't think you need to go there.
... some work 
eventually it would still make sense to switch to the Unity / UE4 wagon instead. Porting your character tech to those should be surely possible, and you get TAA, AO, etc. as well. However, personally i really like to see people still develop custom engines!
) 
