Honestly, the keys that are "missing" (arrows and homecluster) are present on a 60%, they're just there on a function layer.
After a while of use, you honestly won't even realize there's no physical key, it becomes second nature to just hold the function key down and press the new key-binding for them.
For example, on my
kbt pure, I just hold Fn[penguin] with my right thumb, and
Up - o
Down - k
Left - l
Right - ;
Delete - Backspace
Home - ,
End - .
PgUp - j
PgDwn - m
As for the rash, I'm a nurse. I'd recommend you see your GP/whatever your alternative is to one where you live

I highly doubt it is due to the keyboard, if anything it sounds like some sort of allergic reaction to some clothing(although it seems a bit strange to be just under one arm).