Thats quite a list, and it doesnt exist,you've got way too many constraints to make anything that is fast. If you do you'll end up with a really slow, heavy boat and you've only got 5 months to build it, so, I think you'll need to start with an existing platform. If you want to beat Randy and the Russian, you have to start with the premise that your sailboat needs to be fast, faster than an inflatable and more proven than Randy's folding trimaran.

I would start with an Acat, and modify it and beef it up. Go find a used, older Acat. Its light and fast enough to beat the Russian and as fast as Randy's tri, and if you are not looking for the latest/greatest design, you will find a bargain. I would chop down the mast or consider a two part mast, (find a broken one and fix it, make a 2 part mast.)and a reefing sail (take a used Acat and modify, plenty around) If you really wanted speed, add a spin, (do a search for Acat with spin, there is a Dutch sailor that has video posted and its impressive) A spin plus an Acat is the fastest all around cat design I've seen. Go find a used F16 spin, or a used F18, HT, or something similiar. You will stomp on the Russian and leave yourself lots of room for the portage and the upriver parts.

Portage
Flip the acat upsidedown, attach 2 wheels so the boat is balanced, and pull with soft harness a bike or walk/jog. Is a skateboard for rollng down hill worthwhile? and jog/walk the rest? A bike seems too heavy, I would go for lightness and speed to win. If you keep the boat assembled, you could pack all your stuff on the tramp when its upside down.

100 Mile upriver
Can you row this? Can you sail upriver? Can you add a kite - like a kite surfer - kite. Light and fast. This part has me stumped.

Good luck.

Bill