your last paragraph has 2 questions in it (2 different projects).
Im not sure what you are asking. #1 seems to be about a supercharger, #2 doesnt make a lot of sense. Heat is just something you are going to have to deal with. There is no magic trick that will make heat ONLY be your friend
Small turbo = more heat. Your exhaust temperatures are not going to change as long as you are out of boost though. Higher temps generally come because you are burning more fuel.
I dont believe you can coat the wheel, and realistically, if you coat the housing, the coating is going to get worn off by the turbine blade where they come close to each other. There are some efficiency gains but I think the $ would be better spent on a nicer turbo or better gauges or left in your pocket, etc.
You arent going to see gains from this kinda stuff unless 5 hp in a 500hp motor is a big deal to you.
The biggest "efficiency" gain you will find is using a larger turbo. Larger turbo just meaning pick the turbo that will make the HP goal you have. Probably ported heads will help some, as well as different cams. Both of those would cost the same as doing all that coating, and have much larger gains.
If you dont have a HP goal, then you need to figure one out. there are some turbos which are just too small for our motor no matter how low your goal is. There is a guy who just put a 16g on. That is decent for 350whp goals. Now if you have a 350whp goal and you want to use a 9b mitsubishi turbo, you will never make even 200whp with that turbo.
Get a power goal, then go on franks turbo calculator at turbomopar.com......try some stuff out on there, then maybe ask people when they think your specific turbo choice would start spooling on our motor. Then you can get more realistic #'s. I already had my turbo car running so i knew what RPM I was getting what boost. That made the calculator very easy to use for me. I did find that I picked the wrong turbo (my first turbo) though. Too much exhaust turbine.