the lights are too little either way you go...the 50/50 will give you a more oceany feel but that is about it...if you want corals (including zoanthids) you are going to need a new fixture...you would be better off going for PC or t5 rather than a bunch of t10 or t8 bulbs. additives aren't going to help the zoanthids, they need light
reef trace adds elements to your water which may be benefitial in terms of the worms tube building but aren't going to do a bit for it as far as feeding...reef plus may do something for you and it may not. feather dusters are tough to feed because they have very specific size requirements for what they will catch from the water column
not sure what a "pink sea cucumber" is, perhaps Holothuria? no matter what, a sea cucumber would be a very bad choice; first, they are not filter feeders they actually process the substrate (they eat a bunch of gravel, suck out the goodies, and spit the gravel back out) and the amount of stuff in a ten gallon will not sustain one. second, when it dies (as it inevitably will) it will relase some really toxic stuff into your tank which will be very damaging in a ten gallon...all and all just a poor choice