Thank you for posting the plague mask pattern! I love the fabric set you made your first one from, and the grey + rainbow looks almost iridescent (I think that one's also yours, and not a reblob). One suggestion - have you considered paper piecing for the patchwork outer? You could do paper piecing straight onto the printed interfacing, which would prevent errors in the initial piecing/flat work without really changing anything else about the final construction.
I have only tried to do foundation paper piecing once, and the process was so unpleasant to me and my graph-paper-plotting, math-doing, always-press-the-seams-open sensibilities that I basically repressed the knowledge that the technique existed. But yes, plenty of people have used the technique and had it come up great for them, so if it is your preferred method, go for it!
Also, the grey and rainbow one is mine (I was going for the very cliched modern-quilt aesthetic of neutral+rainbow solids) but it is the design I have seen most emulated. I guess it is harder to get a complete set of Kate Spain’s Central Park line than it is to get a spectrum of solids.