Hello,
I do not think the focus will ever handle as well as the fiesta, If you want a car that handles and can be used in time attack then a puma entered into the pocket rocket class should be fun.
Staying with the focus your only real course of action is weight reduction, putting in bucket seats and a light weight battery would be a good start, for safety as much as anything else. I assume you are also going to be fitting larger front brakes, if so I have a selection that I could do you a deal on and if you find yourself on my side of the bridge you would be welcome to pop in and have a look. Not sure if you have read my thread but both of the focuses I bought had worn out clutches and were the weak point.