CBR150R mileage : 40+ in City / 45+ in highway for sure. I even get 45+ in city also, but as always said it depends on your riding style.
Comfort: good for both
Riding in traffic: I dont see as a problem now since i got used to it.
highways: I love it
Maintainance: I dont rip my bike, keep it under sun or rain, rash ride on road: I do regular service, regular wash, regular check on brake oil, coolant level etc. So,there is no major issue popped up so far.
Long life (engine): needless to say about superior honda engine quality.
Long life (body):can't comment now. Will not trouble you much, you can take other bikes from Honda stable as example.And why dont you consider Unicorn?. Anyways...

You will hate riding CBR atleast till 2000 to 2500 kms in odo because of improper gear shifts and lack of torque. I would suggest not to take the CBR in city trafic before some 2500 kms in odo. So right after the first service whenever you get time , take CBR to open higways, get yourself acquainted with bike's features.

I also travel 30 to 35 kms daily to my office. I would prefer public transport rather my bike as it saves me money spent for fuel and energy wasted under sun in polluted atmosphere. See if you can go by train or bus for three days in a week and enjoy riding your bike at the weekends or in days when traffic would be less.
this is my experience in 6200 kms done and counting, my own, my love CBR150R. use your discretion to buy you one of it.