There are many car parks around (Luminy, Baumettes, Gardiole, Callelongue, etc) but if I can give any good advice, WALK there from the last bus station you may found in the vicinity. :
1) the place is nice
2) your car won't be torn into a mere amount of broken glass/steel relict, everything having been stolen before.No matter if you show an old "caisse" all covered with bumps and rust, for they'll get away with the wheels...Unless you hire an armoured division to look after it.
Marseilleveyre (432 m) is the highest point of the western section (west of Morgiou). Mont Puget (564 m) crowns the eastern massif, more close to Cassis.
3) North-central/east sector : around Luminy University campus, take bus 21 (Canebière - Luminy).
There should be more possibilities : ask RTM (Régie des Transports de Marseille) - they have a website, but uneasy to manage, unless you already know the town well...better to phone.