Hi, you could take a look at those here
Generally speaking I would say there are much easier ways to break your performance than vertex count / material count… =)
And those costs also depend on other things, so its not like some mesh with 10000 polys will always cost you the same (e. g. vertex shader, dynamic lightning or not, overdraw/overshading so the mesh topology and due to overshading then the pixel shader, …).
So you could also watch through this here An In-Depth Look at Real-Time Rendering - Unreal Engine
so is there any other way except build a demo including every types of objects then running on various platforms, then modify the account of objects, do many test then have a estimation before the project started?
There are a ton of free marketplace assets including levels at the marketplace (and also sample projects from epic under the learn tab) which you can download and profile (see how they perform and look at their assets)