You will need to get yourself a refractometer so you can make sure you get the right salinity. They sell hydrometers...but they are bad and when I used one my salinity would fluctuate greatly. You can order them pretty cheap off of some sites and ebay.
When you get this and mix your water, you can just mix it up in the tank the first time. After that, you need to mix it in an external bucket or something and let it sit for 24 hours to make sure it is all disolved. Any salt that isn't disolved can burn fish gills and harm coral. I do a 10% water change weekly through 5 gallon buckets, though in yoru case I'd just do 2 gallons weekly.
The small whisper will probably help out, I still like HOB filters, especially biowheels, for additional filtration. Though since you already have a 10g tank along with the 16, right? I would look into turning the other 10g into a sump to give you some extra water to your system and a safe place to do water changes through since dumping water into the display can cause some havoc and be stressful.
