BCG and Barrel are the most important, definitely lean more towards the barrel though if accuracy is a big deal as diminishing returns are more prominent in the BCG. I would also highly recommend choosing a barrel with a Mid-Length gas system, there really isn't a need for a Carbine system especially if you're shooting a barrel thats 14 inches or longer, and the added recoil impulse of a carbine system just ends up being something you spend money on other parts like the buffer system to mitigate.
After that, a good muzzle device would affect your shooting the most (if you're doing more action style shooting). Maybe a nicer buffer system like a VLTOR A5, Geissele Super 42, etc.
Things like fancy charging handles, mag releases, etc are just quality of life changes that aren't important to start with, but are nice to have later down the line.
As far as the Aero BCG, it should be good to go. To be honest, I haven't had any issues with any BCGs I own, ranging from cheap no-names to Colt Canada, as long as they have properly staked gas keys you shouldn't have any issues. The fanciest I own are a Colt Canada BCG and a Faxon Lightened BCG, with the Faxon being the only one with an appreciable difference (that being reduced weight).