It's pricy to park in Gib, so it's worth considering leaving your car in Spain. As for sightseeing, I can recommend the tours offered by the local taxis drivers, who will show you all the bet bits and save you money. Walk towards the cable cars and they will approach you. We were initially a bit wary but were so glad we opted for it. It's not too long a drive from marbella, expe if you use the toll roads, but set off early and leave late in order to avoid the massive customs queues.