… five-fingered hand is an accident, not inevitability. Many ancient amphibia had 6-7-8 fingers, but their descendants did not survive until our time. Imagine how beautiful a piano concerto for 8-fingered musicians would be.
5-fingered people would be considered suffering from oligodactyly (oligo-, having liitle + daktulos – finger) and “normal” people would be amazed that they can do almost everything, such as walking and writing.
2 hands + 2 feet body plan is not an inevitability either, just a result of a fish with two front and two tail fins crawling on the land. The ancient fish had different fins arrangement, including extra pairs of fins. I think two pairs of hand would have increased the brain size as well – probably we would have colonised the Solar system by now.