20 metres of CAT5e will incur no loss. Cat5e can manage Gigabit over 100m of cable and would represent the best solution.
Perfect world -
1. CAT5e socket at each end and use infrastructure cable
2. Then use simple short patch cable to connect cables
the sort of faceplate you would use, back boxes for wall mounting are available. Copper cable
CAT5e solid core copper should be used between the sockets. Krone tool
for connecting cable to the wiring blocks.
In terms of instructions just match the colour scheme of the connection blocks on the socket, or if you want to do a quick job or temporary test then tool less connectors like RJ45 Gigabit Connector
at £6 each are worth adding to the toolbox.
If you need to colour match your Ethernet cable for décor reasons then people like BlackBox do different colours http://www.blackbox.co.uk/gb-gb/fi/1234/11407/GigaBa...