2001 Century, 3.1L engine, automatic transmission, 90k miles

Owner recently replaced intake gaskets with updated version and replaced coolant. Battery and alternator recently replaced.

​​​I am purchasing this car from someone I've known for many years and trust. I haven't owned an American made vehicle in over 20 years and most of my automotive repair experience has been with older Honda Civics.

Hope to get a heads up on common issues (such as intake gaskets) with this car and also suggestions for routine 100k mile servicing. Here's what I intend to do soon after purchasing it. Please comment for or against the following and add suggestions or advice. All comments are welcomed and I won't be offended in any way:
1) 3x3 ATF drain and fill (no flush machine)
2) Replace primary o2 sensor(s). No current CEL light , but imo they are inexpensive and weaken over time degrading fuel trims and mpgs.
3) Considering replacing some or all coolant/hoses after 10k miles of ownership.
4) Replace thermostat and bleed coolant
5) Replace spark plugs with oem
6) Drain (or suction out) power steering fluid and refill with oem
7) Replace any worn vacuum lines