if you pass your test, I would advise you drive a small car until you learn to drive on your own. Driving with someone sitting next to you telling you what to do, is entirely different when you drive on your own for the first time in todays traffic, and you have to make the decisions on your own.
To afford a Ford focus you will need to have a full time job, plus your insurance will be high as a new driver, plus road tax, mot, and servicing.