During the startup of a new tank the use of activated charcoal or zeolite can help in avoiding algae by removing ammonia as it forms. But, the same can be done just by heavily planting the tank with fast growing plants from the beginning. An exceptiion may be when you use ADA aquasoil as a the substrate, where some ammonia is leached from the substrate - then the charcoal, etc. will be useful for sure. It isn't certain that charcoal or zeolite removes enough nutrients to be concerned about - it isn't likely that it does.

You don't need to worry about excessive flow dissipating the CO2 in the water. As long as you don't create heavy rippling of the surface water you won't lose too much CO2.

Soilmaster works very well as a substrate all by itself, but it doesn't do any harm and might do some good to add laterite or river silt or garden soil to the bottom part of the substrate. The best way to do this is to mix it with the SM in the lower section of the substrate.

260 watts of CF bulbs is more than enough for a 75 gallon tank. Half of that is adequate for most plants, assumiing the fixture has good reflectors, which, at that price isn't likely. So, you probably have about the right amount of light using all 260 watts, assuming poor reflectors, if any.