That is pretty good cord and will make life easier for you - nothing worse than trying to untangle a mess of cords in pitch black morning with frozen hands. My experience with it is that it can come untied if not knotted properly.
The weight has to hit bottom and must allow the decoy to move freely in the water to make the whole thing work - mine are about 30 - 36 inches long as I do not hunt in deep water situations. I don't recommend tire weights - I bought lead weights that can be bent around the decoy's head in order to minimize tangling lines (there are other styles too) - it is a nominal cost and you'll be a happier hunter with a weight designed specifically for its intended purpose.
The decoy is going to drift with the wind so make sure you tie the cord to the keel at the front of the decoy, thereby putting its face into the wind like the real things do. When you put them in the water, leave a space between two groups of decoys for the ducks to land. They are social creatures but need a 'runway' to glide into. Ducks land into the wind so position your decoys and yourself accordingly. ( I usually get all set up and then the wind direction changes - durn it.)
Noted your other post concerning the fact that you had bought a dozen decoys - suggest you get at least two dozen more. I usually hunt with four or five dozen dekes this time of the season and then cut back to about two dozen late in the season (and call much less aggressively) as the ducks become more and more decoy and call shy. Here in S Texas we get several different kinds so I have pintail, teal (both blue and green wing) and mallard (even though we don't get too many green heads down here) decoys.
You may want to hunt with someone who has hunted ducks successfully before you go it alone - there is a lot to be learned - as with any type of hunt...... But beware - it is HIGHLY addictive - you get to boomboom a lot. You have just scratched the surface with expenditures to date.
Good luck with it..