What is the minimum amount of equipment required to "stub" for a whole house generator?
When I hear "minimum" I think "trying to save money".  

Do you really, seriously, plan to buy a large 50 KVA generator with an aim toward powering the whole house so you can have life as normal (except for the insufferable roar 24x7 of the machine?)  Will this run on natural gas or many trips to the gas station for this thirsty beast?  Reason I ask is if you only plan to use a smaller generator to power important loads, this all gets a lot easier.

In this case, you install a main panel in the normal way.  Then you run a large, say 100A**, circuit to a generator interlock, then to a subpanel, then you punch down all your generator-desired loads into the subpanel.  It can be quite a large subpanel, in fact we recommend that.  (Don't be the guy who counts circuits to figure the smallest panel to get, that saves very little money and adds a lot of cost later.) 

A lot of subpanels can be their own generator interlocks.  That makes things cheaper still.  

For instance you could even have two interlocked subpanels 100A** each, at sane cost, and simply put every load them with none on the main panel (except loads that would be completely insane to put on generator, such as a Chevy Volt charger.) If you had a 50KVA generator, you could power both!

So it really is a matter of pricing the different options.   



** speaking of pricing, you might also consider 70A.  70A breakers are much cheaper than 100s, and remember, you need 3 of them per subpanel.   By the way, the subpanel can be larger than the breaker, so for instance a 70A breaker can feed a 225A subpanel.  You'd do that to get more spaces.  Spaces are very good, and cheaping out on spaces is a bad idea.