We've built over 100 of these farmhouse beds - we've tweaked the design ever so slightly.
Our first Farmhouse Bed took roughly a day to complete. We sanded the entire bed, applied stain & then applied two coats of matte varnish. At least apply one. Stain can leak for weeks, and smell bad for longer.
We use 2x3's for our slats and find them extra strong!
Then we applied A matte polyurethane - We also used metal caps on the holes in the top of the footboard/headboard.