Admittedly this involves avoiding a lot of annoying fights (read: save scumming), but major sources of possible Day 1 income includes:
(ED: Just ran through this myself)
50 G from the skeleton in the Abandoned Shrine, 150G from Hydrangea (Lack of Flavor) quest, 500G from the 2 Star Metal (one in the semi-hidden hole/cave in the south part of the central forest, one in northern forest cave), 100G from the chest in the lower northern forest, loose change around the Ogres and Mothercrow (~176 total), and 500 G from the chest next to the Ogre Commander.
In Normal you can also count the two Duelists, but as you say, in Nightmare it's kind of a wash since even goblins will wreck you at first (tbh even the goblin fight with Albrecht is a bit RNG-heavy). Still, that will put you at about 1300-1476 G (depending on if you collect all the accessible coins on the ground), which is sufficient to afford all 5 BW @ 1040. I don't feel like it's an absolute necessity to buy them, but if it's part of your plan it's best to do that Day 1.