LONDON, Oct 28 (Reuters) - Man Group , the world's biggest listed hedge fund firm, is planning redundancies that could number 180-200 as it cuts costs after a fall in assets and its takeover of GLG, a source familiar with the situation said. The cuts would amount to around 10 percent of the two companies' combined workforce, although the final number is yet to be decided, the source told Reuters. Man bought smaller rival GLG Partners for $1.6 billion this year after seeing client a