He's really cute! Chestnut is a term for "not black"-- there are an almost endless number of shades of chestnut ranging from the darkest liver to sandy golden. I would call your boy a chestnut... but another name that often means a lighter/brighter shade, used in stock horse breeds, is sorrell. Sorrell IMO is just another word for chestnut, but it might be more descriptive based on your colt's shade and his breed background.
I would also say he has sabino-- which makes his white markings big and flashy-- ie. Taller back socks with "points" on the front top edge, a big blaze that covers his muzzle and lower lip.....
As far as roaning.... his sire appears to be a snow cap, which means that most if not all of his foals will be born with app characteristics and they will usually do some appaloosa roaning as they age. Its hard to say how much or how fast-- it really varies by horse. Also, sometimes horses with sabino will roan--- its not related to the appaloosa genetics-- its a seperate process-- your boy could actually eventually roan because of both sabino and app genetics, if that makes any sense, LOL.
I don't know if you have this, but here is a link to his sire Incognito--- scroll down to see his photo. stallions