500 meters may or may not be "sniper distance." Green fucking Marine recruits, many of whom have never held a weapon, much less fired one; qualify with open sights at 500 meters. Dude's background was auditing/ accounting; so he didn't necessarily have the military training, but he damned sure had the equipment to easily pull off a 500 meter shot.
Re: targeting Aldean: According to his girlfriend, Paddock repeatedly cased Las Vegas Village from different windows in their room when they stayed at the Mandalay Bay a month before the shooting.[16] Paddock also may have considered attacking other events. He had researched large-scale venues in cities such as Boston since at least May 2017[15] and had reserved a room overlooking the August 2017 Lollapalooza festival in Chicago, but did not use it.[17] From September 17, Paddock stayed at The Ogden in Downtown Las Vegas, which overlooked the open-air Life is Beautiful festival that ran from September 22 to 24.[16][8] Paddock's internet search terms from mid-September included "swat weapons", "ballistics chart 308", "SWAT Las Vegas", and "do police use explosives"