Around 1/2 in 10.The quad is extremely unlikely - probably we'll win one of the FA Cup/PL Title/CL Title. Winning two of these is a bit unlikely - winning all three is I think on the order of 1 in 10 or worse.
Premier League 60% (sneaking upwards as each game goes by).
FA Cup 70%
CL. Break it down into Q/F, SF and Final: 50%, 50%, 40% (cos I think Barcelona will be in the final).
Treble = Call it 4 in 10 because it's all 'rough'
Quadruple = 4 in a 100, or 1/2 in 10