Wayne,
depending on where you are rafted depends on whether you are advised to use shore lines...let me explain, if you are the 2nd boat in the raft then shore lines work very well along with the normal springs and breasts onto the adjoining vessel, if, however, you are then the third or 4th rafted boat things get a little complicated as the heights of the vessels and lengths can make things a little tricky as the shore lines will need to extend outrageously.
Because of the tidal flow a Southwold shore lines of course are preferable but if space is tight and you are the third rafted vessel it won't be commiting the biggest sin if you only use a bow and stern breast lines and springs to the inner vessel. (Ensure that the inner vessels aren't leaving before you though as they will set you afloat and ensure that they have substatial mooring lines)
As for rope - 14mm three strand will be fine - 16mm for a 33ft boat isn't necessary nor cost effective for long shore lines, and long lengths of double braided 'woven' rope stretch considerably under load!!!
Hope this helps