Me no expert in SPS but i feel it is exactly easier to keep SPS in big tank as the water volume is higher, the water parameter is more stable and allow more room for mistake.
parameters control
Dosaging pump will solve the chemical issue like kh, can and mg. (sunny intro a cheap dosing pump maybe u can take a look).
Cost
1)The only thing is need strong wave, if go for votech or tunze will burn a hole in your pocket, or u can use a lot of cheap sun sun wave maker, then cost will greatly reduce.
2)high electric bill, but since u r using Led should be quite ok.
Just some of my view. Cheer.