You can look through this thread as there are many sample fares down to the satang. My best estimate for a metered taxi would be 425 - 450 baht all in, including the meter, tolls, airport fee.
No clue but maybe ask on UBER TH web-page or Facebook?
A lot of people are complaining here about UBER's "Surge" pricing.
When I use:
https://www.uber.com/fare-estimate/
I get:
Suvarnabhumi Airport Passenger Terminal Complex, Samut Prakan Millennium Hilton Bangkok, Charoen Nakhon Road Bangkok
Your Options:
uberX฿575
Nearest UberBlack฿1,075
Sedan฿1,075
SUV/MPV฿1,075