to the OP, it seems like youre a level headed individual for a kid.
keep up the good work.
i have a 16 year old, he's been around all kinds of hotrods muscle cars and ford diesels.
i am a firm believer that Chevys are junk, but thats my opinion, and i only have experience with gasser chevys.
im also a biased F series owner for over 20 years.
i would tell you that get what you can afford.
find something you wont have issues with.
this is what i told my kid.
he found a 61 F100. I-6 and a 4 speed.
SUPER easy to work on, decent fuel economy, and parts are super cheap.
you dont need a diesel for your first rig, but if thats your choice, i wont be the one to hold you back.
everyone wants to have a bad@$$ rig as a first vehicle, but as i told my son, plan on wrecking your first vehicle.
he loves his truck. and he's almost ready to start driving it!