Sir If NGK, BKR5EYA-11 is the no, if denso, K16R-U11,IK16,VK16 are regular, iridium power and tough with a gap of 1.1.
Do not worry in rain water, car will adjust the gear according to speed or keep it in "L", that is 1st or "S" second gear, also good for climbing or towing, in Civic its "2", will lock the shift in 2nd gear, also good for acceleration.
Keep the Car's electrical system in top condition, you cannot jump start it if its battery failed.
Do not rest your foot on brake while accelerating and do not excessively change the shift positions, leave it in "D" and do not leave your foot of the accelrator while the gear is changing, like we do in manual cars, it will confuse the torque converter, keep steady acceleration, listen carefully to the reverse chime indicator and do not look down while shifting, while parking pull the parking brake first and then shift in "P" mode, in long traffic jams shift to "N" the clutch will disengage and save you some fuel.
Get a 100K check done from Toyota Southern motors, will not cost much, they will check all filters, fluid, electrical, valve clearance, belts, brakes, fuel lines, A/C/heater, ECU etc.
CNG is ok, get a nice EFI kit, if possible a sequential one with an inflex 50kg cylinder, get the work done by a good installer, I can recommend you one, keep your air filter and battery/spark plugs in top condition for CNG and run on Petrol after every 500km.
And please do not drag with an EXI PROSMATEC, you will loose.
And congratulations in the end, you have purchased a better car then a 0 meter XLI at half the price, believe me and take good care of it.