I have the next model up from the 320 and I can guarantee you won't be able to keep any corals in that lighting (1 11w PL lamp) apart from non photosynthetics. I wouldn't suggest using the under gravel filtration either for that matter, there nice looking tanks but you need to gut them to use them for a reef.
I removed the lid from mine, added in a skimmer and a much much larger filter. I also replaced the light with a clip on 150w metal halide so as to allow me to keep coals, though really you don't need something that over the top (I couldn't resist LOL)
The 320's only 28l, but from memory it's like 40 cm tall right? So something like a compact fluorescent totalling about 30-40 watts would be good, and allow you to grow a variety of corals, but I doubt it would fot in the hood. Maybe there's someway you could modify the hood to fit in more lighting?
If not about the only coral you could really keep is a sun coral and they aren't really beginner corals due to the amount of care they need, but I started out with one, its not too hard to care for, just takes time.