plastic bull nose edging for the forms, to give a nice rounded finished edge.
Really have to resist the temptation to mix it soupy, you don't want a weak concrete that will shrink a lot, the counter top will crack.
Its much harder to finish the stiff acrylic modified mix, so you'll have to work it at the proper timings. Also, the edges will most likely need pointing up with sand mix, as the stiff mix wont vibrate down very well and you will have some trapped bubbles on the edge.
Form up right against the walls, that way you end up with a countertop that fits perfectly without measuring anything, and no moving. Put felt against the wall as a slip sheet, so the concrete doesnt stick straight to the paint. You will want to use a cement board on top of the cabinets as a base, and be sure to wet it, or prime it with a bonding agent, so the suction from the board doesn't rob the water from the cement mix. You will want to form the overhang up to suit your taste, can get creative here and use the premade plastic edging, or use beveled strips of wood to do a bevel edge. Mix outside. Truck the mix in 5 gal buckets and carefully dump.