For around here I think 30 to 50 meters of 3 strand nylon about 12 mm diameter would be fine as an anchor line. In practice the chain on its own will usually be enough.
mooring lines you want at least 4 about 10 - 12 meters long .Nylon is considered good as it stretches a bit in use so absorbing some of the shock load in sudden gusts of wind.
A pair of longer mooring lines are usefull for mooring against harbour walls about 20 meters each should do.
Adds up to about enough to go from Cardiff to Swansea,are you sure all your lines need replacing?