The accessories are available individually but stock is unreliable.
If the gearwall slats are screwed into wall studs, then the hooks should fit snugly into the gearwall limiting movement when tools are hung or removed. If the hooks come off, no worries, they will easily fit back into the grooves.
You will need to also purchase the Guardian rail that those pieces snap into. Also, I would recommend runing two 2x4's from the steel roof beams to the floor and then a horizontal 2x4 between them to screw the rail to instead of screwing into the resin walls. Suncast makes shelf and storage hooks systems as well that would mount directly to the wall but all the ones I see at HomeDepot.com say they are for shed series other than Vista.
Yes you can lay it over plywood, but you need to put a #8 Screw of sufficient length to go through the plywood and into the wall stud. One screw in every track at every stud. It can take a lot of screws depending on how much track you hang. Two inch screws will work when applying over 1/2 inch plywood or drywall .
I don't believe that will work. I believe they are different enough that they will not work.
Gladiator hooks and accessories will not fit on the Sears versatrack, however the Sears accessories will fit on the Gladiator wall tracks. I have both and they are good products but most of the Gladiator accessories have an extra tab on top that tucks under their rail. It looks like you could cut that tab off in order to fit the Sears versatrack but I haven't tried that yet.
No tracks come with this kit, only what's shown.