Whew! A 3500HD as your first manual trans.. mine was my very first car, a '65 Impala with a 4 speed. I taught myself to drive manual in that car. Coulda used some guidance but I got it done.
Just take it slow, especially the shifts, that NV4500 transmission isn't sporty by any means and will have a relatively heavy shift "feel." They're tough transmissions but do have their issues; if it grinds between any of the shifts it will need attention before it gets worse. The one in my '93 3500 currently grinds between 1st-2nd so I've been double-clutching to ease it between gears.
There used to be a great 3500HD-specific web forum (3500HD dot com) but being a sleepy niche forum, the guy that ran it finally shut it down due to hosting costs and the headaches that come from running a web forum (spammers, hacks, etc.) A few of the regular members there are here as well, so there's some 3500HD-specific knowledge carried over, and you'll find a few here are working on their own 3500HD projects. You probably did find the best place to be, IMO, for these trucks.
Richard