'Andrea will paint the bedroom soon' 'Andrea will soon begin to paint the bedroom.' There needs to be a word between soon and begin, so if you want to keep it in this format you could say 'Andrea will begin to paint the bedroom soon.'

It depends on what you want to say. Some people procrastinate. So maybe you want to want to say Andrea will begin to pain the bedroom soon. In this situation, Joe's answer is the best.

Perfectly understandable but not really a natural way to express what you've put. Instead you could say, Andrea will start painting the bedroom. Andrea will begin the painting of the bedroom soon. x

What you wrote, Anna, is perfectly correct

That is perfectly correct.