Radhikarefer this link you will get all your doubts cleared regarding sip,http://cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080b29.html

Leebasic thumb rule of this is to have same schema and structure so you can not have a diffrent version of CCM integrated to same AD.thks

hi,the quality of voice will not be a worry if you are trying any qos in it and by stacking 15 switches i dont think there should be any issues regarding redudency.

make CTI port a member of the pickup group defnitely it will work.

hi,I defnitely dont agree with this main reson is if are haveinga seprate VLAN then you will be getting diffent VLAN address so which is help full for trouble shooting problems in the same time by haveing diffrent vlan you will allocateing diffrent ...