Well...you already made your decision, but here is my half-cent opinion, anyhow...

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First, I disagree with TTF. I think that a hatchling corn is the perfect first snake. Why, you may ask? Because, yes...they can be flighty, and even a bit bitey...but this will help to prepare you for properly handling your snakes.
I agree 100% with your own assessment of watching him grow. It really is the only way to know 100% your snake's every attitude. You learn their feeding response, their handling response, their reactions to your presence, and all the other "finer points" of each individual snake, and these things will vary from snake to snake, even of the same species. They also TEACH you the finer points of handling snakes, and will better prepare you for the inevitable future purchases of a variety of species, because you will get more snakes, and you will expand your collection beyond 1 species. Everybody does.
I keep kings, corns, pituophis, BPs, and boas. My favorite snake to handle and "hang out with" is my boa. Second would be my BP. Third would be my kings, followed by corns and then pituophis. My favorite snakes to keep would be my corns followed by my boa, than kings, pituophis, and BP. Notice the difference? Yes, boids are more calm in hand, and easier to "chill" with. But the care requirements are much for finer in scope, and they do not respond well to mistakes. Corns are exceptionally easy to care for, and are VERY forgiving to the inevitable beginner mistakes that everyone makes...no doubt. Even small mistakes can put the average BP into a downward spiral of food refusals, bad sheds, tempermental behaviors, and aggression. Corns will usually recover fairly quickly from common rookie mistakes, with little residual or lasting effects.
Also...adult corns tend to be very calm. My adult female is a gentle lamb. I take her to my daughter's pre-school class to share with the kids. She is more "trustworthy" than my BP. I wouldn't
dream of letting 15 3 year olds pet and handle my BP, because I am quite positive she would never eat again from that amount of stress. My yearling through adult corns take it all in stride. When I bring them back home, they hide for a few minutes, than return to their normal selves. That level of stress would probably permanently and negatively effect a BP, IMO.
So, really...all I am doing here is confirming your decision, and letting you know my opinion and experience, and how it relates to your decision. If you are getting a hatchling corn, I think you made the right choice. :cheers: