As previously mentioned wheel balancing and alignment, for just fitting bigger wheels.
But if lowering the car on springs
Then adjustable rear camber bolts are advised,
Steering limiter kit is advised when lowering the car on 18" rims or bigger
due to the 18" rims being 8" wide compared to the 16" wheels being 7" wide the wider rim inside a lowerd arch can rub off the arch when turning full lock either left or right.
Finally if fitting coil overs then you require,
Front adjustable strut top mounts
Rear adjustable camber bolts
Ford steering limiter kit.
I've purchased the steering limiter kit from ford for 15 pounds the steering limiter kit is blue but defo wont be seen when fitted because the sit in to the CV joint grommet to restrict turning by a couple of mm.
Came with ford fitting instructions for the C-Max but all models of focus are the same in that department, hopfully upload a pdf copy of the fitting instructions for the steering limiter kit in the coming weeks.