Just to chime in on the batching thing from experience on Unity 4 (i know we are talking about Unity 5 here but i have no idea if it's been fixed) batching just didn't work at all (we had pro on all projects) and we ended up using the combine children script to actually get round this issue. It might be fixed in Unity 5…
I found a script (combinechildren) somewhere on the unity forums, i think, that combines meshes that are static. I guess it reduces draw calls and stuff, so you can design your environment, and simply combine this to a big mesh and keep your original meshes in the scene (deactivated ofc) for later use and editing. Could…