Crossing are not possible in this setup because it would derail the trains. I can add some just for visuals without collisions. You can transport water, diesel and fertilizer/herbicide in tank cart
You can use the Soaring Eagle SA30 Drive-Over Conveyor, from modhub, put it in a long hole under the track, it works. I used it near FIT Plon in a previous sellpoint, the hole is still visible in my map
But agree with you for other liquids :-)
And also a flatcar width equal to engine width, flatcar without backrest if possible!