Plo Koon was a long-time member of the Jedi Council, and well known for his piloting abilities. He often tutored Jedi in dogfighting. That said - since Battalions are generally led by Majors, with Army Groups consisting of several battalions, he was likely something along the lines of a Regional Commander. I'd be very surprised if his duties and responsibilities were limited strictly to air combat - in fact, I'd bet his taking to dogfighting was protested by his staff.
As for your question regarding ground battles:
SW Databank: During the Clone Wars, the Neimoidian Home Defense Legions doubled their conscription rate, and called up all reservists for active protection Neimoidia and her purse worlds. As such, the gently swaying bridge-cities became filled with Neimoidian tanks and airstrips, mansions became billeted with soldiers and gunners, and polished skyscrapers and gilded towers were marred by anti-starfighter emplacements.