A trickle filter/sump can burn off C02 if there is a lot of splashing. Plants only need a total of 12 hours a day of light. Anything beyond that is not needed and will only make it tougher to battle algae.
If you have actinic lights, there is no need for them in freshwater. If you want to keep the tank low maintenance, (you have a pretty deep tank to be constantly reaching in to prune plants) stick with slow growing plants. I would keep the lights at around 2.5 watts per gallon of water for 12 hours a day. As I understand it, MHs only cover about 4 square feet. Your tank is what, five feet long? It would be better to have two MHs of lower wattage. (two 250 watt bulbs spaced evenly would be perfect) Use a simple clay gravel substrate with perhaps a little peat on the bottom, and a moderate level of C02, 15 tp 20ppm max. Refer to a pH/KH chart to determin your C02 level. http://www.aquabotanic.com/charts.htm
All the substrates Gomer mentioned are basically clay gravel. Clay is used because it is inert, contains mostly iron but possibly other minerals, and it is capable of absorbing nutrients from the water.
If it were me I would use cannister filters instead of a sump. Have two instead of only one. Feed the C02 into a external reactor connected to the outflow of the cannister filter.
For plants that you do not need to prune often, go with Swords, ferns, Anubias, Vallisneria, Sagittaria, Crinums, Cryptocorynes and slow growing stem plants such as Lysimachia, Nesaea, Ludwigia glandulosa, or stem plants you can trim without having to up root and re plant, such as Micranthemoides, Hydrocotyle, or Cardamine. Smaller grass plants could be used which will spread out on their own without a great need for re-planting or thinning to often. This would include E. tenellus and dwarf sag, or even hairgrass if it is not shaded by other plants.
You can seed the substrate with fertilizer tablets for minerals as well as NPK, (nitrogen-phosphate-potassium)