Chosen Solution
Could it cause a problem to replace a 16Gb i7 with an 8Gb i7?
From a hardware perspective there is no difference between a 8 GB Vs a 16 GB system. But! Having less RAM can effect what you can have running concurrently and/or the size of the app and its data. Your OS will try to leverage your drive for Virtual RAM so if your drive is very full it can’t leverage it to make up the difference from your 16 GB logic board. You may need to clean some stuff off freeing up space. A 128 GB drive needs about 1/3 free a 256 or 512 GB needs about 1/4. You may want to think about getting a larger drive.