You can deduct medical expenses at your charge in Geneva (even if foreign bills). You’ll simply have to convert from EUR to CHF using the rates here https://www.ge.ch/taux-donnees-fiscales. For income, annual average FX rate is used. It is widely accepted by the Geneva tax authorities.
Keep the medical bills/proof of payments. They can be requested by the tax authorities.
In some canton, they won’t ask for receipt for some amount, it’s not the same as a deduction “forfaitaire”. (And depending on your ethics it is or isn’t ok to deduct that if you haven’t actually donated anything)
Depends on canton, you should follow your canton’s tax manual. ZH’s rule is to apply 40% depreciation per year from purchase price. You declare purchase price and year and 0.6**(years of ownership)*price as value. So, basically after 8-10 years of ownership the car would be almost entirely written off and that’s OK.