If you have the option buy a better inverter, the one you bought is pretty low quality.
Cheapest one I could find:
Axpert Type Pure Sine 3000VA Inverter Trolley + 2x 100Ah Battery (8 HOUR BATTERY LIFE) KIT - 3000W (50A PWM SOLAR) (150-200 cycles) for sale online at the Best Prices! Door to Door and Overnight Delivery
www.geewiz.co.za
These Axpert inverters are pretty robust. I have one install running with an Axpert since 2015 and still going strong and plenty of people on PowerForum running them too.
Re the long lead. It isn't a problem unless it has nicks and it is shorted. I assume when you plug it into power you have no problems.