[Tindomul]

Most successful vivs are kept with 80% humidity and are misted daily. This is done for the plants and animals(often frogs or animals that drink only dew drops). False bottoms achieve a separation of substrate from water, and keeps the soil from getting water logged. Another, and much simpler to me, way of achieving this is by using Leca and gravel of sufficient thickness to keep the soil moist but not wet. The soil should be able to wick water up, but not so much that it will be ever wet. As for Orchids, I can't help you much there. Many orchids are mounted epiphytically and therefore depend on regular misting and ventilation to stay hydrated, and to keep from getting root rot.
Water features, in my humble opinion are a good thing becuase they help you control the water level, if it gets too high you can suck some out straight from the water feature. A terrarium with no water feature can lead to water logged soil causing much plant devestation.

Hope this helps. What kind of plants did you try, and what were the conditions like in your failed attempts. Also, what are your standards? What do you consider a successful tank??