The stock radiator and fan system is sufficient enough for turbo charging the engine, however now with the addition of hot and cold turbo pipineg space is limited and it will be difficult to route piping properly with the stock fans. Its recommended to use slim fans, fans designed to be a lower profile with adequate CFM to keep the radiator cool.  I have personally found a 14″ fan and 12″ fan can fit, but its a tight fit, the 14″ fan while  having the highest CFM it does have a higher profile and takes ups some space.  Alternatively, two 12″ slim fans is adequate while allowing plenty of room. For the King6 Turbo Mx6, In 2019 I have changed the setup to two 12″ puller fans on the back side of  the radiator and one 8″ pusher fan dead center of the radiator behind the hood latch. This setup has proven to keep stable engine temps and run the fans for a very short amount of time to keep the stable temp.

The stock thermostat your engine is already equipped with is fine for turbo charging the motor and you should see no problems. If you live in higher temp climates and/or turbocharging while keeping a A/C system, the 170deg thermostat might be a consideration if your having higher then normal engine temps.

Types of fans, fans ive found there are 2 types of fans expensive and cheap. I personally have only used cheap fans under $50 for a pair and have not had any problems.  Expensive fans may have advantages far as CFM, longevity and design thickness and are worth considering.

Styles of Fans: This is more of the more important aspects of the fans.  Witch are curved blade vs straight  blade.  Ive used both styles and i prefer the straight blade design.  As with everything the 2  have disadvantages and advantages.  The curved blade are usually more common and cheaper,  the design sacrifices some cooling CFM with the curved blade that is designed for less noise.  The Straight blade has a higher cooling CFM with more noise then the curved blade. Personally, I have found the noise difference unnoticeable.

The stock expansion tank is sufficient for a turbo setup, however it has some flaws..  its design limits its ability to relocate and mount, and its made of plastic and prone to cracking/leaking. Even on a stock engine, they can break and cause a uncontrollable coolant leak. King6fab has designed a replacement made entirely from aluminum that will replace the stock tank and is a nice upgrade for convenience and peace of mind.