Direction to go for this

I’ve been making games for a while but I’m new to Unity. I’ve attached an image below (however rough and simplistic) of a scene I want to create in Unity. I’m thinking styled a little like Farmville 2 but a little more realistic, a bit less cartoony. I will eventually want to get the different plants swaying in the wind, etc. I will also be animating plants growing in the field. Eventually, this will be an app running on a lower-end galaxy tablet in the 200 dollar range. I realize I might just have to learn by trial and error, but I figured it wouldn’t hurt to ask a few questions here. I’ll start with one question:

How detailed should I go with the models? For example, if you look at the bushes that border the field, I imagine each of those being a textured flat, rectangular poly. Same with the trees. But I start worrying that the ‘overdraw’ of so much alpha will really slow the renderer down (especially when you look at the trees and see how much alpha space will be in there. So, it makes me wonder if I’m going to need to build flat ‘cut-outs’ that follow the outlined shapes of the plants, reducing or eliminating the alpha. But I do want to indicate shadows in some way, whether faked or whatever. Or would I be better off just going full-on 3D? Keep in mind that I don’t want to go full-on realistic in style. Even if I had the time, that’s not the style I’m going for.

Any thoughts would be helpful. Thanks!

2744189--197833--MM_UnityQ_1.png

Might consider mapping to a 3D object that is a similar 2D extruded shape. Since you are going for a 2D look - the 3D object will have the silhouette shape of the 2d art and have the 2D art applied as a texture. This would overcome the overdraw issue.
Best is to just experiment - since the art is relatively simple - could create actual 2D sprites, 3D silhouette shaped objects with 2D textures and real 3D objects placed in the scene to look 2D all in 1-2 evenings.