My two bobs worth
Update the condensor(s) if required, renew the hoses as required, add a 10" thin line scimitar (curved) blade thermo fan (or two but probably not necessary) on the rear engine lid condensor. They are aerodynamically more efficient, and look cool, but I couldn't find a scimitar fan when I was doing mine. The 930 has a square condensor in half the wing because there's a funny radiator thing that takes up half the vent space, but you get the idea.
The scimitar fan
I wired it into the compressor circuit, to cut in and out with the compressor or you can wire in as a manual switch to turn the fan(s) on and off as required (as PeterM said, above 60kph turn it off), wire in a compressor bypass to take advantage of the centre vent fan when AC is not required, update the evaporator, if required or consider the retro-fit half kit to move the evaporator from under the floor with a more efficient fan and gain passenger leg room.
If you keep the evaporator under the floor consider modifying the drain at the bottom. The factory grommet design (pictured below on rhs) encourages water build up and possible overflow onto the carpet. I sikaflexed the grommet in place then sliced the inside part of the drain grommet off so it was flush with the inside surface of the casing. Also some evaporator cases don't have a front dam and can overflow should the water build up above the drain grommet, particularly when accelerating. Mine didn't so I added a dam made from perspex. Also the case join is a potential source of leakage. Rusted clips is a giveaway.
Here's another dumb thing that Porsche did.
This is the fan speed coils mounted directly in the vent, restricting the air flow. The pictured set up is in LHD cars, in RHD it is in the curved vent pipe after the evaporator (Pics 3 posts below). I think they did this to keep the resistance coils cool, but who knows. It doesn't appear to be as restrictive in RHD cars but it's there, well it was. I now have a motor with internal speed control. (above). At the top left is the tube that the old fan speed coils were mounted in.
EDIT: and in the plastic container at the top of the pic is the old coil pack.
I think I spent more than two bob, hope this helps.