Do I need a soundcard for gaming or will onboard audio be just fine? I plan on getting an upper mid-range motherboard with 7.1 audio channels from a respected brand like Asus/GIGABYTE/MSI/etc.
static noise from the motherboard can be solved using a DAC, a sound card generally won't help with that.
People buy sound cards to power higher impedance headphones which can give clearer audio on said headphones.
What motherboard and headphones do you have?
Generally completely unnecessary unless you have good headphones, most motherboards should have a decent or good sound chip on them.
you dont "need" one. people buy add on cards for extra features or if they can hear excess noise from the on board sound which is rare. i recommend getting the board you want and if you aren't satisfied, you can buy an add on card at any time anyway.
static noise from the motherboard can be solved using a DAC, a sound card generally won't help with that.
People buy sound cards to power higher impedance headphones which can give clearer audio on said headphones.