I've never even seen a 18ft Parker. Yes I have installed several windless's on boats
I find a 18ftr to be rather small for installing a windless, but you may have a bad back?
This is the one you want. It will take 1/4in G-4 or BBB chain....No your hardware store chain will Not work.
You want at least 18ft of chain....I'd just get 20ft myself.
It will take 1/2in rope.....How big is the anchor locker? I suspect it's small.