You're getting a bit ahead of yourself there.

What's likely happened is that you've got one or two bad glow plugs and it's giving you starting troubles.

Since you're determined to change everything, then just do the glow plugs and you'll find that a fresh set of Bosch or Beru will give you superior starting performance.

You don't need the afterglow relay on the 617..........it's just money that's wasted..........unless there are other problems with the engine.