I do it almost the same way, but I move the vaccuum from one spot in the gravel to another each time it looks like it has most of the mulm ( "poop"etc) from one spot. ... I hope that makes sense...
I keep doing this the whole time until I have about 50%of the water out each week.
also, I always put the dechlorinator in the water i was going to add, b4 I added it. Either way works. To Add water back, make sure the temperature of the new water is as close as possible to the old water and then add it in gently. The set up I have now lets me put the bucket full of new water up higher than the tank and use the gravel vacuum to siphon the water back in slowly. I like this because it doesnt stir up a lot of gunk into the water and send the plants flying around
Oh also remember to unplug the heater before you take water out, and Remember to plug it back in when through!!
Oh about plants, look for low light easy care plants. plantgeek.com, or ask in the plant forum here... java fern and java moss are the two I rely on, but there are others too. I wonder what problem you are having with nitrate?
I Like the look of your tank btw