You can keep 1 mandarin in a very well established, very mature 58 gal tank with tons of rock rubble. I know, I have done it for over 2 years - BUT - as stated in the previous threads - more than 1 mandarin will fight and a pair will probably not get enough to eat even in a very well established, mature tank.
My bigger concern is that you are planning on keeping 4 pots in a 50 gallon tank. These are some of the largest horses, reaching up to 14" long. I wouldn't think you could get a tank in the 50 gallon range with adequate height. Also, as previously stated, these are cold water fish, needing a chiller in most places. I'm unsure whether the mandarin will survive the temps.
Probably, you should do more googling, reading, and looking.