Matt obviously has very tough fingers – I would advise 5mm dia for the main halyard.
Some people use a bobble on the end, but I prefer a shackle – you can sew a small eye into the rope with a sailmakers needle and thread, either way iyou can haul the headboard right to the top of the mast.
And I would agree on the genoa halyard, you should have wire and a muscle box or highfield lever to apply the tension. A decent dinghy chandler will be able to supply a wire genoa halyard made up with the fittings for either option. I would guess the highfield lever is cheaper and easier to fit – but in operation is less sophisticated and requiring more strength.
Assuming you carry a jib – you will probably have a shorter luff, so just get a wire strop made up for the difference.