keeping the balance fore/aft, or getting closer to 50/50 is a big part of weight reduction. When I went thru this process with my Mustang, I scraped all the sound deadening material off the floor pan, removed the insulation from the carpeting and trim panels (I kept the trim panels since they weight almost nothing once all the insulation is gone), radio, HVAC, speakers, rear seats, seat belts (installed 6 point roll bar with competition belts), replaced the front seat with a Carbon/Kevlar, took out as many brackets and stuff that wasn't needed, and removed the entire factory wiring harness. Once everything is out of the car, I started to put things back in, but keeping in mind the placement of those items. Moved the battery to the rear passenger side to offset the driver, ran all the wiring along the passenger side, and mounted things as low in the chassis as I could. Anything that could easily be moved lower and rearward was done to try and counteract the weight of the engine and the fact most of the weight reduction happened aft of the firewall.
What sucks about doing massive amounts of weight reduction is that the daily driving level of the car drops. Sit in traffic on a hot summer day with no HVAC and no insulation on the floor. Things get very hot very quickly! It also gets very loud in the car since you are now sitting in a tin can. For the few dozen times a year that my Mustang leaves the garage, it isn't too bad to live with. I would not want to go the same route with my Fiesta, unless it was a dedicated track car.
Back to the OP, this is where I would be looking for weight reduction based upon what I have seen on competition Fiestas;
Seats (front replaced with lightweight versions, rear removed)
Sound deadening
Trim
Carpet
Factory seat belts (again, assuming this is a track car only)
A/C compressor, lines, condensor
All brackets to hold trim, console, speakers, rear seats
Radio, speakers, amps, wiring
Exhaust resonator
Muffler
Lightweight battery mounted in the back
Lightweight wheels
Lightweight brake rotors (2 piece) and calipers (unsprung weight savings is always good)
Air bags (assuming this is a track car only)
Polycarbonate rear door windows (remove window motors and cut rear door inner skin)
I wouldn't waste money on a carbon hood or decklid. The factory hood is already fairly lightweight due to how thin it is, and the rear hatch is taking weight off the wrong end of the car. Both items are expensive and that money would be better spent on brakes and wheels. Rotational and unsprung weight savings will get you big increases in performance. Any heavy object farther away from the cg will also make the biggest difference in terms of handling.