1) Yes but your wallet will hurt far worse than it will with a standard laptop.
2) No. Yes if you have a $7000 BGA machine, a source for the RAM, and don't mind potentially destroying the board. I never tried, total waste of time IMO.
3) I am unsure.
4) No. Inside this model the graphics is integrated into the CPU. You could put a faster CPU on but again, $7k BGA rework machine, potentially destroying it, and since this is a haswell model that integrates the PCH into the CPU you would have to redo the SPI ROM with a clean ME region so the SPI ROM would properly communicate with the PCH. This is way too much work and misery and hassle, so no no no no no.
These are insanely fast machines, by the time 8 or 16 GB of RAM is too weak you will want a new one anyway, so I would say do not worry about it.