Sounds like you are in a position to take on most of the necessary repairs. I hadn't noticed that it was an S... that makes it much more interesting.
Here is my take on your list.
Should be looked into and discussed before buying
The battery was disconnected when we arrived, no idea what that means
Strange noise on startup
The windshield is cracked and needs replacing
Bottle of antifreeze in the trunk (could be nothing, I keep oil and antifreeze in the trunk just in case)
Future projects
Creaking suspension (does it clunk on bumps? My base does which I take as its way of saying "do some maintenance". I had it aligned and the tech didn't see anything untoward.)
Can be lived with
Two tire brands: Michelin Pilot Sport All Season and Cooper RS3-G1, all from 2021
(The good news is that the tires are good. I have often run with different tires front and back, but given my little old man driving habits that doesn't cause any problems. Your use may be different.)
Both side mirror motors do not work (adjust manually)
One of the headlight sprayers is missing (buy some paper towels and windex
The convertible motor is slow and sounds tired. May need replacing soon (is it slower than other Boxsters? May be normal and converting it to manual is free and isn't much of a hassle)
The front bumper seems misaligned (may be misinstalled, there are a bunch slots and such that have to be properly assembled. Or could be the result of broken mounting pieces.)
The plastic undertray on the front bumper is partially disconnected and scrapes on the ground occasionally, particularly when reversing (I think all Boxsters have broken undertrays... just to varying degrees. Remove them and put them back after you get around to fixing them.)
The rear bumper is cracked (not that difficult to repair... I used fiberglass on my front bumper cover (and undertrays))
The driver's seat is torn and needs repair or replacing (put seat covers on till you have the time and/or money)
Appearance... how important is this to you? Can be taken care of over time and will not affect the performance on the windy bits of road.
The clear coat is peeling, there are hail dents and lots of scratches and scrapes. Just about every panel has some kind of damage
The plastic trim by the windshield has hail damage and needs replacing
The clear coat is peeling on all four wheels
All of the Porsche crest center caps are damaged in some way
Most of the lug nuts are rusty
Rubber gaskets around headlights look dry-rotted
I hope some other forum members will chime in with their opinions (although having the opinions of 78F350 and I is a great start... well having 78F350's opinion is a great start...).