Since it’s your first car, I’d mostly focus on keeping the BMW 120i (E87) clean and reliable before doing mods fix that oil leak first because German cars can turn small issues into bigger ones if ignored. After that, light cosmetic stuff like a subtle rear diffuser, good wheels, tint and a proper detail will improve the look without hurting resale value. I’d avoid anything too aggressive or expensive since it’s a daily and just keep it simple, maintained, and slightly styled rather than heavily modified.