"denominator is not of the from (1+xxS)(1+XXS)"
If you like such a form (and I would agree with you for solving the present task), you have nothing to do than to find the complex roots (s1 and s2) of the denominator equation D(s)=0. Then you can write D(s)=(1-s1)(1-s2).
EDIT: Regarding the three other questions - I have some problems to understand the meaning. Stability parameters are defined for systems with feedback only. For all stability calculations we need the loop gain. Here, we have a given transfer function - and that´s all we have. Hence, these three questions make no sense, unless a feedback loop is shown.