Please don't mix stainless steel and steel chain or you will get electrolytic corrosion. Also when you are putting on the shackles there is a way to put them on so they tighten when they nag not loosen, but you should still mouse the shackles.
If you are going to buy a buoy avoid the ones with a metal rod up the centre with an inflatable collar, I have seen the rods break and the collars shred.
If you go with the type where you pass the chain up the center and it had a plate to hold it in place, put a big knot in the chain so if the plate fails the chain won't drop.
I keep my 7.4 on a fore & aft mooring when afloat which has a main load baring line connected to the eye with a quick link and a second safety line
loose over tubes made off to the cleat.
This was on the YBW site and quite of a few of them seem to lay their own.
Hope it helpd