If you can weigh the cloth that was provided in the package, you can calculate the weight per unit cloth in oz/yd2. A weight around 6 oz/yd2 is good for tip to tip, and a couple of layers or a 1/3, 2/3 pattern can be used. More than 10 oz is harder to work with.
Heat from the motor won't be a big deal, but you don't want the epoxy softening just due to the sun. An epoxy such as West shouldn't be used for that reason (a Tg around 120°F). Use an epoxy with a higher Tg. Aeropoxy is one, and there are many others.
Whether or not you need tip to tip depends a lot on the material used for the tube itself. Tip to tip helps to keep the fins on the tube, but more importantly, it keeps the tube from deforming. If you are using a fiberglass or carbon air frame, you might not need tip to tip unless the fin span is more than perhaps 3" or so. If the tube is cardboard or blue tube, then tip to tip will strengthen the tube itself.
Jim