Welcome to ribbing!
In answer to your questions,
1) I could not verify the model number, but it sounds about right, they most likely consider the boat 14 ft in length.
2) All Novurania boats use Hypalon for there tubes. Novurania is known for
making a high quality boat. They market them as tenders to the yachting set and as recreation boats.
3 &4) You can try a heat gun, it should work fine. Be sure not to touch the fabric with the tip of the gun. If any residue remains, try MEK (from any hardware or paint store) on a clean white rag. Wet the rag with it then rub the tubes. Turn rag as needed, and stay away from the seams if possible. For cleaning the tubes, I have had good sucess with a product called "Roll off"
which you can get at any good marine store.
I would avoid paint unless the tube are really in rough shape. From ypur pictues, they don't look too bad. After you have cleaned them put a coat of 303 protector on them. You can find that with the roll-off.
Good luck with your rib!