When I raced my Fiesta it came with a brake booster, in fact all of the Fiestas (3) that I owned had one. If any came without I don't recall seeing any.

Just did a quick check at RockAuto and they do list a rebuilt booster for the Fiesta so you should be able to get one through them or other sources.

I used synthetic gear lube 75W-90 with the stock diff and with the Quafe when I installed that. One thing that I would mention is if you do happen to open up the transaxel is to check out the internal shift linkage. Twice the linkage failed on me at the track when a retaining pin failed. It was a simple fix but it required you to remove the transaxel to fix it. The second time I drilled the hole bigger and used a bigger roll pin.

The first time the trans was stuck in 4th gear and the other time in neutral.