Gearbox.
Good gearbox, crap first gear ratio.

Yep your flywheel is fine. Most prefer a lightweight one but the standard Rs/ Zetec one is fine.
Clutch, yep the Frs Ap racing clutch is ideal.
Mods for this to work. A longer clutch pivot pin from Gbs/kitspares around £20 or Westfield made a thrust bearing spacer at around ~£100. This is because there is a 20mm shortfall. Finally you want a spigot bearing ~£10.
Only the top five bolts connect to the engine, this is fine. There is a big chunk of alloy on the bottom of the bellhousing that I shave down in a kitcar. You may not need to in the Sierra.

Engine,
Sump, you have options here but I am not a fan of the 30 year old cvh sump. Best avoided. They absolutely worship a guy called Neil Dunne on Fb and in the banger racing world.

Engine mounts, I buy laser cut plates and make my own. There are ways to use cvh.

Water pump, There is no factory reverse pump for a Rs/Blacktop like there is a silvertop but there is an aftermarket one see Ike engineering or most just run an idler See Da Engineering or Retroford amongst others.

Water rail,
I am not a fan but you won’t have much choice in the Sierra. If you fancy the raceline one do your home work. I’ve tried one twice and could not get it work well. Besides it’s unlikley to fit with a turbo (top mount).

Turbo,
your very unlikley to get one on the standard manifold between the engine and chassis leg. It’s going to have to be a top mount.
On a budget, a chopped about ford Zetec manifold works nicely upto and around your target power.

Inlet, if you can clear the steering and chassis leg the Rs one will work nicely. I chopped the elbow of and blobbed a new one on forward facing. Injectors are 440cc and will just about run to 300bhp according to Sabre tuning .

Exhaust, I run 2.5” but will up it to 3” for 300bhp.

Engine managment, I even use the Focus Rs.