I'd suggest just a 2S pack since it's such a small model and the motors that would be suitable for it will generally have a higher Kv rating so for them a "big" prop would be in the 7 to 8 inch range.  And for a folder I'd want to maintain about that sort of size.  As for the motor the model will likely come in at around 8 to9 oz with care.  maybe 10 if the kit wood is fairly heavy.  So a motor with 40 to 50 watts of power handling will do just fine.  On 7.2 volts from a 2S pack that's only 40/7.2= 5.6 amps to 50/7.2= 7 amps.  So the motor will be one of the smaller and lighter options that weighs roughly an ounce.  And you can afford to keep the pack down to one of the new and light 800 mah 2S options and save both weight and size.