The FSA BB would not be compatible with 6800. You'll need to remove (unscrew) the FSA megaexo BB and fit any Shimano Hollowtech 2 BB (Tiagra,105,Ultegra,Dura Ace) to work with the 6800 crank.

The chain might not need changing either. It all depends how much it was shortened when it was installed. Alot of times, factory bikes come with chains that are too long. So you might be good. I would try it first. Before spending money. If the chain is too short. Only the big/big combo would likely be unusable. That combo is easily avoided. Even if its temporary until you buy a new chain.

All the others parts will work fine. They do not need changing.

The FD may need to be re-positioned higher to clear the 52t chainring.