I wouldn't worry about the memory. 12GB won't improve performance at all unless you are filling 8 (which is doubtful). I would definitely get that SSD. It's a really good upgrade for a laptop.
CPU, I wouldn't change it. Basically if you want a faster CPU it's better to get a higher end model to begin with. Later on if software gets too far ahead you might want to swap the CPU out but it should be much cheaper at that point.
GPU is pretty much the same as CPU except you probably can't change it anyway. The GPU cooling system is slightly different for each generation so you can't just change it.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…