When I install Cuda it says "no supported version of visual studio was found. Some of the CuDa toolkit won't work properly" do I have to download the whole visual studio or there is a zip file around
You don't have to install CUDA Toolkit(it's CUDA, not Cuda or CuDa) for Cycles GPU rendering to work. You need to have Blender(installed or portable version - it doesn't matter), your GPU has to be supported and its drivers must be installed. Latest drivers have the highest chance to work, if there are problems, one might try previous driver versions. CUDA Compute Device must also be enabled in the User Preferences, System tab as well as the appropriate device or devices must be selected, also GPU Compute needs to be selected as Rendering Device in the render settings in the Properties Editor, Render tab.