I would get a full size case rather than a midsize case - better cooling.
Get a gold certified power supply.
Consider at least another hard drive.
What will you be editing?
DSLR footage mostly. Maybe along with some after effects renders. No crazy 4k or anything like that
Get the 2GB.
so you asked a few days ago which one, i responded and made some other hardware suggestions. you really need to change the psu and seagate hdd. they are not "solid reasonable picks" even for a budget. yes they may work but you are asking for trouble with those parts. Building an editing PC. Which GPU should I pick?
as far as the 2gb vs 4gb, i haven't seen a 2gb version of the gtx 970. the reference card is 4gb. if you need to save money, there is the gtx 960 2gb.
I suggest you get atleast a 700W PSU with that configuration. A 500W wont be enough.