The door cards (covers) are textile-covered in the Turbo. There are special upholstery cleaning sprays available. Generally you spray cleaning foam onto the fabric, rub it in carefully with a sponge or a soft brush to remove dirt, let the foam dry and finally vacuum it clean. Depending on the manufacturer, you may need to repeat this process once or twice to remove all dirt. But before foaming the entire door card, first test the product on a hidden area (like behing a removed armrest) to see if there are any side effects (discolouring etc.)
As for the noises, you should first try to locate where they're coming from. Some of the squeaks maybe caused by broken fittings, allowing parts to vibrate. Almost everything is fitted by all sorts of plastic clips that are easily broken when interior parts are taken apart. Obviously you need to replace all broken clips with new ones.
Then there is the poor fit of some panels. Even if the clips are fine, two panels can still contact creating noise. Also some fittings may wear or become loose, caused by the vibration of a heavy panel (like the dashboard). You can try to silence these noises by putting some silicone sealant between such parts. It's elastic, yet 'tightens' things up. But notice that the sealant also 'glues' the parts into place, so it may be difficult to remove them in future. You should also choose a transparent sealant, just in case you 'spill' some...
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If some cables behind the dashboard cause noise, you can try putting some foam-plastic around them. Make sure that the choke cable doesn't rest on the rocker cover, it sends the engine noise very clearly into the cabin. (I don't remember if the choke cable is routed over the rocker cover in the Turbo, it is in my GTL.)
All in all, it can be difficult to completely silence a 9 interior. My 9 has all its dashboard fittings intact, but still the dashboard shakes up and down visibly when I drive over a very poor road surface. Plus the body is structurally so flexible, it flexes the plastic panels no matter how well they're fitted. Driving on some old cobblestone streets in town centres, I can barely hear my own thoughts! It's like sitting inside a huge drum during 'Also sprach Zarathustra'!
To avoid rust on the outside (painted surfaces), wash the car regularly, at least twice a month if you can, more often in the winter if there's road salt where you live. You should also apply wax polish 2-3 times a year, it's essential in protecting the paintwork. It's not just for creating a nice shine, it also seals little stone chips that would otherwise start rusting rather rapidly. For example, there are tiny rust spots (originated from stone chips) on the lower parts of my 9's doors. They're almost microscopic, I'd say 1/10 of a millimeter. They're most visible after the winter (there's LOTS of road salt for 4-6 months here in Finland). But when I use a good wax polish every spring, these rust spots 'disappear', you can't see them with a naked eye. I wax polish the car again in autumn to give extra protection for winter. This way, I've avoided having to have the doors repainted or welded even, for about 10 years. Had I not done anything to them, I probably would have needed to replace the door panels buy now...
To protect the underside of the car, make sure the rust-protection sealant is intact. If not, repair it. Renault used a PVC sealant, which protects well from stone chips but is a bit tricky on the other hand; The PVC sealant can look completely intact, but if rust has gotten under it somewhere, it can rapidly spread there hidden. And when you can finally see the rust through the PVC layer, it has already caused extensive damage.
For hollow body sections like the sills, you may want to spray some rust-protection wax inside them. There are many brands here in Europe: Teroson, Waxoyl, Dinol etc. Also make sure all water draining holes are open after spraying, or that dirt or tree leaves haven't blocked them.
Finally, try to avoid leaving a damp car into a closed, poorly ventilated garage. Such combination can trigger rusting process very quickly.
Hope this is of some help,
Juha