Congratulations sir.u got urself a very nice car... hope u ll enjoy it for long.
well, to get to the point where i CAN say something, let me say that i cant help with the sound system and windscreen cleaner issues i have no experience with either.
your car is brand new.you HAVE to drive on petrol for the first 5000kms.because this is the 'running' period of the engine.u can only consider cng kit after doing that.
while doing this 5000kms, keep an eye on the fuel economy.i can safely say that it wud be around 11-12km/ltr in local driving.well, dont panic.thats ok.all cars give bad mileage and performance when totally new.the mileage starts getting better AFTER 5000kms.depending on the driving habit and traffic etc, it will go upto 14km/ltr (went there for my car) in local driving.thats pretty good i wud say.
so, decide about getting cng after 5000kms.the avg mileage on one cylinder on cng will be around 140km locally and 160 on highways.and one cylinder should cost 500rs easily.the difference in cng and petrol is, very, pretty noticeable after the recent price hike on petrol.50km a day is the boundary line.someone driving below it should NOT get cng and someone doing more then that should.now u have to decide urself.
CNG wont really harm the engine anywhere before 2 lakh kms (or u can say it will start harming the engine from day one but u wont be in trouble before doing 2 lakh kms) so i think u dont need to worry about the engine.
now do that maths and decide urself!