300TE purchase advice

[Merkey]

Hi Everyone,
Great forum you have here... I'm impressed!

Ok, looking for some advice on a '88 300TE Wagon I looked at recently.

The car will be for my son who is 17.

So, its a 1988 W124 300TE Wagon. shows 64,000 miles.
Has sat for the last year due to the owner getting fed up of it stalling out when warm. Sometimes restarts immediately, sometimes after a few mins. Owner says it can sometimes be prevented from stalling by slipping into N and reving.
Battery was dead flat, but after carefully attaching jump leads, started on the first crank, instantly.
Ran smooth until it got warm where it began to miss/hunt a little and looked unstable. Reving cleared it and it was fine after that.
Drove it a short distance only cos its in Non-Op, but it felt OK and didnt stall.
Owner says has replaced or checked all the normals. OVP, cap and leads, had pump and relay cleaned, replace potentiometer.
Still does it.

Other issues:
Dead battery.
Water light on dash on... is that Radiator or washer fluid?
SRS light came on and didnt go off... we just sat and didnt have seat belts on.
No cold air from A/C. Maybe needs a recharge, but can you easily retrofit 134A?
Brakes dragging/ rotors warped.
Rear muffler rusted out.
Should there be a shield under the engine? I saw a clip on each side but nothing attached.
Little or no service history, but looks like it was cared for.

So, what am I looking at here?
I need some ideas of what else I should ask/check and some idea of what the cost of fixing the issues it has.
I am a pretty competent guy and will do most myself. Kinda concerned about it sitting so long though.
Any advice or pointers or knowledge would be gratefully accepted.
Thanks in advance.