Since you’re going hotswap, you’ve already got about 3mm of space on the back of the PCB. if you make your case just a tad taller, your battery could fit under the PCB.
unfortunately, using a Xiao makes this approach less than ideal. The Xiao’s battery connector is a pad on the back, reducing the amount of space a battery can fit.
I use purpz on pinkies and thumbs, then silvers everywhere else. I can see how the 10gf differences between Reds and Silvers might not seem like a lot, but it was noticeable for me. There’s also the Pro Reds which are slightly lighter at 35gf. After that you’re into pink/purpz range which might be too light.
Boards with surface mount diodes are most likely using 1N4148W SOD-123. I think there might be variations of the corne that don’t use surface mount diodes, so make sure the one you’re getting supports them.