Wheel building for polo

If spoke length calculators give me 286.6 length will 286mm spokes be ok with 12mm nipples or should I go for 288? Since I'm gonna build the wheel myself I'm thinking I'll skip crows foot and try 4x, am I right in thinking this will give smaller gaps than 3x?
Based on your calculations, I'd go for the 286mm (I always round down).