I am about to start my first wheel build for my fat bike. I will be using btlos carbon 65mm rims with a measured 537mm erd nipple grove to grove. I will be using 2.0 / 1.6 / 2.0mm (14/16/14 gauge) double butted DT Competition Race spokes. My hubs will be hope fatsno 197 x12 rear and hope fatsno 150x15 front hub. I do not have the hubs in my possession but feel confident that hope posted specs will be the same from hub to hub. Waiting on my hubs still. I used Musson's spoke calculator and worked out 260.9 nds front, 261.1 ds front, 262.9 nds rear, and 261.1 ds rear. Am I correct in assuming that I would purchase 48 262mm spokes and 16 264mm spokes? I would buy some extras for each to have on hand. I will be using sapim 12mm chrome brass nipples. I asked the rim manufacturer if I should use nipple washers and they said it would be up to me to either use them or not. I already have a stash of washers. What is the consensus on using nip washers? Does that rounding up look right on the spokes?