draw calls practise and performance for mobile , need help!!

first i'd like to apologize for my bad writing skills , i'm not a native English speaker , so i hope i'll be clear in pointing out my ideas.

what is the best practice to reduce draw calls for mobile devices, can you share your technique with me?.

before i start explaining, i don't use any compacted shaders only mobile diffuse , anyway i have figured out an idea , i haven't tried it yet. let's say i have 8 different objects with 128x128 texture for each model , each object has its own material, let's say i want all of them appear at the screen in the same time, , i thought instead of using a material for each object , with a photo editor i combine the 8 textures into a one 1024x1024 texture and apply it to a single material and use it for the all objects , then adjust the uv on each model to the mini textures at the 1024x1024 texture, so i have different objects with a single material. is this a healthy thinking in managing draw calls?

another question let's say i have 40 objects from the same model with the same material (duplicated objects) with no collision or any aim to apply collision whatsoever, for example some trees at the background , if i combine them together , will that reduce the draw calls? i tried it and it seems it does , but the problem is that the numbers of polys on the screen increased , because now the model covers the screen wherever i turn or move since all the models became a big one,so what is your take on that? what is more important draw calls or the number of polygons on the screen.

i understand that no one can give me an absolute answer , as all these numbers are not the only factors on performance unless i test it myself , but it would be nice if you answer me based on your experience ,and sorry again for the rotten English skills lol, i can speak English but didn't learn it formally so I'm not good at writing lol.