The precise name for the yellowish bloom that sometimes occurs on concrete slabs and blocks is efflorescence. It's caused by the blocks' concrete reacting with water (rain, surface water, etc.). It's harmless and will go away on its own, but it's still bothersome and unattractive when it appears on a brand-new installation.
Your worst nightmare is an oil leak on your brand-new block-paved driveway. The first order of business is to take immediate action and soak up as much of the spill as possible. Absorb the excess with a towel, cat litter, talcum powder, or cornflour before using regular detergent and a stiff brush. If the oil is pure, it will be absorbed by the ground. Oil with contaminants is a bigger problem. You can use degreasing chemicals or engine cleaning supplies, but you should always perform a spot test first.
Your brick driveway may slump in a few spots after decades of use, or the edge that gets the most traffic may crack. Block paving allows for simple solutions to these kinds of problems. Removing a section of blocks, replenishing the sand bed, and then laying down the same or new blocks is possible. Unless there has been significant sinkage (more than 20mm), it is quite improbable that the sub-base will need to be replaced.
The soil type and climate mostly determine driveway depth. However, the standard recommendation is to use pavers that are between 2 and 3 inches thick.