[Schwag]

Don't bother replacing the hop-up body unless you have to. If it's really old, it might have worn a groove in the top where the bbs feed, leading to jams or the nozzle movement might have worn away some of the inside, causing compression loss.
Barring these 2 things, there should be no need to replace the body, just the sleeve and bucking.

For sleeves and buckings-it depends on the application. A high fps gun needs a stiffer sleeve and bucking. Guarder Black hop-up sleeves are very good and reliable.
For accuracy, get a sleeve with the v-groove in the center. haven't tried them myself, but I've heard good things.

If you want a high-speed setup, you might want to get the madbull shark-fin hop-up sleeve. It has fins to prevent double-feeding.

For a tightbore, madbull makes them good and cheap. However, they have thinner walls than most and because of that, many hop-up sleeves don't fit too well(loose fit). The madbull sleeve I mentioned earlier is thicker to accomodate the thinner barrel.

The reason ICS stuff looks different alot of the time is because ICS uses a split-mechbox design. Some of the parts are compatible, many are not.