I'm not sure if lighting would really be your #1 concern. How would you regulate temperature? In such a small space, I imagine the temp would change drastically. If you had one day where the temp drops below 60 (much less 50 or 40) it would be tough to keep the pond warm. And on the opposite end, any temp over 90 would be really hard to cool I imagine.
Also, how would you manage the water quality? All it would take is a little bit of contaminated runoff that gets into your pond and it would be game over. Not to mention increased evaporation from the sun or lowered salinity from rain.
I'm sure you could do it, it shouldn't be too different than a regular tank, but personally, I think it would be more trouble than it's worth. :/