cat is basically to reccycle the gases in the exaust,it wont affect the engine
i too did it in 2,3 steps 
1.when u feel ur car isnt braking right,get it checked n check the pads status,if not change it at 40k kms,i change mine for the first time since i bought the car,brakes wear out quickly if u do too much sudden & excessive braking,if driven wisely the brakes wud last til 40k kms
2.they should be changed at 40k kms
3.got the oil filter from battle axe shell cantt,genuine is for 650 & the fake copy for 350 though u can go to mondgomery as well to get it even cheaper or to be sure the filterr ur getin is 100% original
about cat service no one told me how to clean it 
if i have to remove cat i have to cut original piping, n if ive to get the sound box aftermerket piping,i have to remove the sound box from original piping,
the easist way out which i see is get a used sound box from bilal jang,n install that in the aftermarket piping 