Great project!
The neat thing about WSJT and even PSK31 is that you don't need to be a powerhouse to make some contacts. (The same is true for all modes, actually.)
Inverted V is a pretty good choice. Is there a particular reason that you are concentrating on 40m? For WSPR, 30m and 20m are reasonably active and provide some very interesting patterns.
In any case, the performance of most antennas improves dramatically when they go from piles of wire on the ground to stuff hanging in the air: there is a lot to be said for "cut and try" especially when it comes to HF antennas. (First principles analysis and antenna modeling programs don't do well at accommodating the complexities of a hill with a house on it, and trees, and leaves, and wind, and rain, and two bicycles in the yard, and so on.)
The bamboo tripod sounds like a neat platform for lots of experiments. Start simple, and get an antenna tuner. You'll be surprised how well non-resonant systems work (as long as you have a sense of humor, keep the transmitter clean, and recognize that the coax is now part of the antenna).