Mobile Optmization Regarding Materials and Blueprint Actors

I’m trying to learn Unreal 4 and for that I’m developing a kind of Tatical Turn Based RPG, aiming for mobile devices.
Working with a flat shaded low poly style, one question come to my mind: What is better? Use a standar texture atlas or multiple flat materials (only vector param) on the same mesh? Which one will generate less drawcalls?

The second question is about blueprint actors, as working with tiles, which tile will have information about it (like movement cost, type, blocked or not, etc). First I thought about creating a blueprint actor with a static mesh associated with it, then I only change the static mesh and the variables within the bluperint. Is that a good approach? My maps will not be big, like maybe a grid of 32x32 tiles.

Thanks in advance.
Lucas Sene