On a 125 for just softies, VHO's may be a good path. T5 fixtures are a little more on the front end, but with the lower bulb replacement costs ($32 each for the VHO's, every six months versus ~$25 each bulb, replaced every 9-12 months). Over time it adds up. T5's can be too much light, though, since it is so distributed (not point like MH, so fewer dim spots in the tank for lower light animals).
Flow for softies can be relatively low in most cases. My bigger softies (tree like softies) generally don't mind being hamered with flow, but do okay in less flow. I generally see larger coral sizes in lower light and lower flow (more due to the light levels-they expand to increase surface area available for photosynthesis, but heavier flows can keep them more compact). Flow is needed (among other reasons) to help remove mucus and sediment from the corals. Softies can close up for days to months at a time to 'cleanse' themselves. When they do this, they benefit from better flow to help move stagnated water around the coral.
As with any reef tank, gas exchange is a very important thing that often goes overlooked. I've had a lot easier time keeping the water quality in check with tanks with good oxygn exchange. Breaking up the top surface of the water helps allow oxygen to enter the tank and keep things happier.
Softies in general are very easy to keep. In most cases, keep water quality reasonably stable, provide at least moderate flow and allow for gas exchange and they pretty well take care of themselves. Beware of the nonsymbiotic sotfies out there, though. Without special care, they are generally doomed to die in the long run (long run on many of hem being a few weeks to a month or so). Chili corals, Dendronephthya's, etc. should be avoided unless you plan to spend extra time feeding (and subsequently cleaning to keep water in line). I don't feed any of my symbiotic softies directly. Decent lighting will provide what they need for food.
I don't add any additives for softies. Keep an eye on the basics (NH4, NO2, NO3) and check things like calcium and alkalinity from time to time (Ca, alk, and Mg become vitally important for SPS and other calcium building corals.
