[5.6.0f3] GI not working

Hello, I built a demo level in the past week to fiddle with Unity. It has a terrain painted with a couple of textures, many objects scattered around the islands, some enemies, etc... It's actually a finished self-contained level, with sounds, animations, scripts... all the stuff. And it runs great on both my development machine and another mac I tried to built it on (despite being at 30fps on fantastic quality there, and 500fps on my machine).

Now, I opened the stats window and noticed that I have over 700 batches. I know little about optimizing unity games but this is obviously too much for a simple scene like that. Granted, I used a lot of free assets with each their own material, textures, etc... so I don't have a texture atlas or combined materials but anyway. For now my biggest concern is lighting.

As of now, there is a single directional light in realtime mode, and NO object is static.

I wanted to try baking lights into a lightmap, so I read some articles. Here, since Unity is constantly changing its menus and options every other minor version, it is impossible to reconcile all the information, as 99% of material is obsolete or deprecated. So, I read about Precomputed Realtime GI and Baked GI. I do NOT have a thing such as Precomputed Realtime GI; there is only a tickbox saying simply "Realtime GI", and if I check that I get all the lights in realtime and nothing changes.

So I checked Baked GI only and changed some of my objects and the terrain to Static and baked it. However, by having the directional light mode se to either realtime or mixed nothing changed. Even if it is "mixed", it only computes everything in realtime anyway and batches count does not decrease. Then if I also set the directional light mode to Baked, it never stops computing (stuck either on Clustering or Light Transport) and I manage to have a scene that is very dull only if I mark like two or three objects as static: shadows are very black and hard and some parts of the models (like the foliage) are not even lit. With this setup, I have about 360 batches, but the game is hideous.

So, how do I exactly optimize lighting if nothing works? There is no realtime precomputation, baking takes ages (actually never finished it for just a third of the scene), realtime is very nice but doubles the graphics workload. And this is only for a very simple scene.