I think a 3-piece would be ideal, as it provides not only the two options of full-length and "storm" length, but also the possibility of different length looms for different sized people or boats. You could have a narrow loom for your SOF and a wider loom for a wider boat. The same paddle could fit several sized paddlers with different loom length needs. As for weight, if it's carbon fiber, it should be possible to keep it down to ~30 oz. or less, though weight isn't critical. The loom shape should be flat sides with rounded edges, with dimensions of 1.5" x 1.25". In "storm" configuration, the loom should be 3"-4" long, with loom inserts to create lengths from 18"-24". I would suggest a blade width of 3.5", similar to paddles made from 2x4s. The overall length with a 21"-22" loom should be ~86". This should give the paddle enough versatility to fit most average sized paddlers, which is what you would need to get the business off the ground.

Of course, once this product does well enough to support more models, a downsized version with a smaller loom (1.25" x 1.0") and narrower (3.0 - 3.25" wide), shorter blades should be offered. A longer-bladed version for taller paddlers could be added as well. Ultimately, the product line could consist of the two loom sizes in a variety of lengths, plus several blade configurations for each, that paddlers could purchase in a mix-and-match manner.