I knit and designed my first mosaic shawl! I've knit one pair of mosaic socks before but never a shawl, what an adventure and undertaking! Monticello is so fun and easy, between each mosaic section is simple garter with only a bit of shaping. I used a single ply fingering weight yarn for my main body and a multi-ply for the contrast.
That means use any fingering weight yarn you want! With a shawl, I have no problem mixing blends and plies I don't think it changes the integrity of the shawl. Shawls don't receive the same amount of wear and tear as a sweater, that is where I would watch mixing my blends/plies.
Monticello is long and wide, so it's perfect to wrap around your neck a few times and let the colors peak out. My tester knit hers opposite and used a gradient for the body and solid for the mosaic and it looks so cool! I'm excited to see what other color combos knitters come up with!