It kinda depends on the size of the spark. If everythign is working right, sparking is common, especially with hi current ESC (they have more capacitance) and/or high voltage. It's not "bad" per se, but can pit the contacts over time. You can use
this page to calculate a charging resistor if it bothers you. However, if you have bad FET(s), it could mean you have a short internally to the ESC. Hard to say without seeing it.
About the charger; are you questioning the balancer wire hookup? For charge settings, just set the cell count to 4. Set the charge rate at 5A, or the cell capacity to 5Ah, whichever setting is used.