Depends on your training provider Most schools prefer to do it all in one go I think, but ask your training provider if this is an option, they are the ones who decide, not us gossiping folks ;-).
average salary depends if you are freelance or employee.... freelance count 45-55GBP per flying hour so depends how busy you will be. 500 hrs in todays climate shouldn't be a problem to gain in a year with possible something near 800hrs, resulting in anything between 22.5k and 44k.
Employee depends on the company, your availability etc but full time employed something in the range of 35-45k I guess