IMPORTANT AFI QUESTION
 

I have a AFI rating and a friend who wants to learn to fly. However, his budget is a bit restricted and asked me whether we can use a private PA28 (with a public transport category on it) to teach him to fly on. Do I need a QFI present or can I teach him and then send him to a club or a QFI for his pre-solo and flight tests?

No way FL I am afraid. I am also surprised you do not know this as it is a favourite question to get asked on a AFI renewal! ;)
An AFI must only exercise his rating within a flying club environment. If you are not an active instructor, chat to a local club, I am sure they will allow you to 'attach' yourself to it for the purpose you want to do, then you would completely legal!