Based on my long history with these vans, having been a fanatic since 1994.
1996 and later models, get a Panlong OBDII Bluetooth adapter ($14) and the Torque Pro app ($5). Allows you to read codes and create additional dashboards showing you everything the vehicle monitors.
Nothing but ACDelco ignition system parts. Too many posts about issues with aftermarkets stuff causing these vans to run funny, only to be resolved by switching back to ACDelco.
Spark plug changes are done through the wheel wells with long extensions and wobble.
Fuel pumps seem to be on borrowed time after 100k. If you change it before it dies, you get to change it on your own schedule, on a nice day, when the tank is near empty, and you can drive it up and down driveway ramps instead of playing with jacks and jack stands. Again go with ACDelco pumps. Too many stories of aftermarket pumps dying early. I've bought a couple Astros with failed pumps that owners had just put one in a few months ago.
1996 and later models, use ACDelco Fuel System Treatment Plus in your van at least once per year. This will help prevent sticking fuel injectors these years vans were known for, which causes the cylinder misfire codes P0300 through P0306.
If you are working on anything that runs off the serpentine belt, make your life easier by pulling the radiator shroud and fan. Fighting to work with those items in place just isn't worth it.
If the HVAC doesn't blow where you want, there is a broken vacuum line. Usually a skinny one, accessible under the hood, that runs around the front of the engine to a junction on the passenger side. If where it blows changes based on acceleration the vacuum line to the vacuum accumulator needs replaced.
These vans like to go through idler arms, get Moogs and be sure to grease them every oil change.
Door seals, to make them last longer, clean and use silicon spray on them.