Q-1. should the gun be taken apart and serviced before use - i think i know the answer to that one.

From Jarhead by Anthony Wofford

"When to clean the rifle
a. Before firing
b. After firing
c. Cold climate
d. Hot humid climate
e. Salt water exposure
f. Desert operations"


Q-2. where does one dispose of unused / unsafe ammo?

Give it to the local police, they will take it to the range
and shoot it up for fun.

Q-3. how unsafe is the corroded caps ammo? can it go boom?

Depends on how corroded. If the brass is just tarnished, it should be fine. If the shells got wet over time, the primer
may be fouled.

Q-4. should i even attempt to use the old ammo? it certainly is inexpensive - and i don't want an explosion.

More likely you would just have a miss fire. If in doubt I would
show it to someone who knows.

Q-5. what's the life expectancy of shotgun ammo - barring any obvious damage or defect?

I have some 12 gauge rounds with paper hulls my Dad loaded in the 1960's and have had no trouble with them. Also some world war I rifle rounds in 30-06 that all go boom and are still accurate.
(Corrosive though, so you have to clean the rifle differently).

I would use those old rounds for practice if they have been stored well, and buy a few rounds of fresh for important tasks.