The most obvious righting line system would be similar to a Hobie 16. Get a line that is good on the hands maybe 10'. Tie each end to your main beam stanchions, but put 1 end thru a ring or small block first. Use a bungee to pull the ring aft in order to take up the slack in the 10' line. You can even make a pully system for the bungee if you like.
When you flip, the line is instantly available to pull on right there at the bottom of the tramp.
Personally i like to point the mast into the wind to re-right a small cat. Just make sure the sail is all the way out and you are on top of the new windward hull at the first possible second.
You could use urethane glue and pool noodles to glue plugs in the tops of all your tubes to keep water out. There are all sorts of possible solutions to the water in the tubes problem including a bigger mast float, but that would not be my choice because of windage while sailing.