I would say pay special attention to gaskets, as mixing of coolant and oil is mostly caused by blown gaskets and that is mostly caused by overheating.
It used to happen with my first engine, and finally i scrapped it.
Dual radiator setup came with the engine from china, yes it came with fan and auto fan switch.
It is similar to these radiators http://ali.onl/TEi
I use Zic coolant in my car as well as bike.