Hi,
For a project I'm trying to power a coin vibration motor which has the operating voltage of 3～3.3V and draws about 80 mA at most via 3.3V pin of my arduino nano. I'm aware that 50 mA is the max current recommended but i tried powering the motor at first before reading about the limit and it worked fine and the arduino doesn't seem to have any problems! 
also I'm going to use the 5V pin for a receiver module and I'm planning to power the Arduino with a 7.4V Li-po Battery via Vin pin. Is this a good idea or should i use separate batteries for my motor?
Are there any better ways to do this whole thing?
The absolute maximum draw from a pin on a 328 processor is 40mA per the data sheet. If you draw more than that the pin you risk that the pin will be degraded if not killed. You should consider driving the motor through a MOSFET. Don't forget a flyback diode.
the arduino doesn't seem to have any problems!
Yet.
80mA from the 3.3V pin is probably fine. If it worked when you tried it then it will continue to work. But it won't last 10 years like that.
it worked fine and the arduino doesn't seem to have any problems!
You have been lucky. Be sure to keep a few Arduino spares around for replacements.
I use up to 50 mA Because if used then there will be problems later
A Nano doesn't have a seperate 3.3volt regulator, like the Uno has.
The 3.3volt supply of a Nano is extracted from the USB<>Serial chip, and 30mA draw is about max.
Not very wise to power a motor from that pin.
Power the coin motor from the 5volt pin, with a resistor or a couple of diodes in series.
Leo..