My grandma gave me her 99 Alero with 3.4 engine which has only about 38000 miles on it. She bought it new. She has no record and doesn't remember what service it has had (except she says it has had regular oil changes). It has rarely been driven for the past 2 years.
I intend to change oil (to synthetic), ATF (probably also synthetic) and tran. filter, air filter, and maybe gas filter. What other service should I do? Does coolant need attention, plugs, other fluids, radiator hoses, belts?
Would appreciate knowledgeable recommendations.

I would be careful about switching over to a full synthetic ATF fluid versus the original Dexron-III. You might consider the new Dexron VI which is a synthetic blend but I have no data on any successful use of it in a 4T40/45E autotransaxle. Works fine in a 4T65E.

If it still has the original Dex-cool coolant then you are due for a flush/change. Dex-cool is only good for 5 years or 150K miles, whichever comes first.