On point1. I can think of 2 ways turning off SC could effect query plan choice (ignoring possible data type oddities or bugs around literal parameterisation).
If the sql contains local variables they will become inout parameters to the LWP and therefore become known at compile time with SC on. This can (and does) change costing and plan choice significantly in some circumstances.
The optimisation timeout will flip to use the 'sproc optimization timeout limit', default 40 instead of default 10.