Brakes on a 1.4 TDi

Hello,

My GF has the above Fabia which has drums on the rear and discs on the front. I have a few questions regarding this:

1, I recently upgraded to 312mm brakes on my MK1 vRS. Could my older setup fit hers directly or do I need to buy new carriers/hub?

2, How easy is it to fit discs on the rear?

3, Does anyone know what size discs are normally on her car?

Thanks.