Win7 home has a max ram addressing of 16 gigs!
Now I'm not sure if this includes vidram in there but if you use home version you will have this limit. Win7 pro,while more expensive doesnt have this issue,as for win8 and beyond I havent found out about this problem as of yet.
Yucca,looking at your proposed build you would have a total of 20 gigs of ram. I would either go with 8 gigs of ram or I would consider another OS. You could get a nice sized storage drive for the price of the extra 8 gigs of ram,this is likely what I would do.
YMMV.