choose what corals you want before you choose light and flow
This is great advice and while I don't want to steal Musho's thunder, I wanted to add that you having live rock does NOT mean that you need to have any special lighting at all - in fact, it will certainly remain 'live' even when kept in the dark. Granted, the coralline algae growth would be inhibited or stopped completely by low or no light....however, arming yourself with this info means that you can get started on the tank long before you will need a more expensive light system. In fact, since fish are not photosynthetic either, many of us will start out with a FOWLR tank and continue to stick to that until we have saved up for the best possible light system; which also affords us some additional time to become more familiar with SW husbandry.
But also take into consideration positioning, corals higher up get more light, corals on sand bed not as much.
Again, great advice and I am not trying to discount it at all, but also wanted to add to this thought by bringing up the point that if you are going to go with the smaller tank and subsequently purchase some of the more 'extreme' light systems (e.g. Mh), putting a coral that it suffering from recieving too much light (e.g. bleaching) on the substrate may not help out as much as you would like since the light coming from a Mh bulb can penetrate water for quite a ways. In fact, this is a great example of why using any 'watts per gallon' rule is really only a basic guideline since there are many other factors to consider. To support that notion, I doubt anyone can argue with the fact that one can keep even the most 'light needy' coral in a 5000 gallon tank without needing 40,000 watts of light...as long as that light is reaching it. Conversely, since light doesn't really 'mix' with the water like a med, suppliment, or other similar things, I could have 5000 watts of light shining on one corner of a 250 gallon tank but if all of the photosynthetic corals I have placed on the extreme opposite side that the light is shining on, the odds are great that the coral will not fare all that well.
Anyways, like Musho said, it is probably best, and probably much cheaper to 'design' your first and then go hunting for the most ideal light system.
I eventually want an anemone. But besides that nothing that light intensive. polyps, bubble and frogspawn have caught my eye so far.
To be honest, I would hold off on the anemone until your tank is not only cycled, but established (as well as until you are 'established' in SW) before adding an anemone since most are pretty sensitive to water quality. Like corals, some anemones will also require different lighting and water flow conditions in order to thrive (but inlike corals, they will simply move until they find the right spot) so that is also something to consider when thinking about lights and power heads.
While I am sure you may already know this, let me say that you should not let anyone tell you that if you have clownfish, you need an anemone, and/or vice versa --- both can survive equally as well in an aquarium without that symbiotic relationship. That being said, it is also very important to realize that clownfish will not host within any and every anemone and in fact, some species of clownfish are not as likely to host in certain anemones, while another type of clown would. Point being, do your research first and then bring home the right combination. Oh, and while I have heard mixed reviews, it is possible for you to buy some clownfish now, but buy an anemone months later and there is a decent chance that they will still host in it. Although, sometimes clowns can be found hosting in certain corals...which, in some cases, can harm the coral.
