It depends on how render-intensive your projects are.
An octo-core machine with enough RAM will often render in minutes things that used to take hours, or than can still take hours on lesser machines.
If your Comps turned out to be something that such a multi-core machine would render in (say) an hour, would that be fine? That's the question you need to ask yourself. And to answer that question, you first would have to create a typical Comp for this project and render it.
Setting up the project and the machines to perform rendering over a network is very easy. See Network rendering with watch folders and render engines in AE Help.
is so should we use window or mac mechines?
Use whatever you like better. AE is designed to perform perfectly on either platform. In any case, make sure you take a look at AE's system requirements/recommendations.