The au naturale look will be OK for a picture frame or a pot hook. Where you will have trouble is working at the counter for a while in a clean white apron. The black "patina" will rub off very quickly onto your apron and maybe all the way down to the white shirt you have under it. It will come off in the washer after a few cleanings but the black will come back again. I vote for lacquer. It will go over "patinaed" copper and come off quickly and easily with lascquer thinner.
You should be able to cut the pipe easily enough but bending it without crimping it will be tough. Don't know if you would be able to do this on a table saw and keep the pipe from spinning or not. Cutting it on a mill with a right angle attachment and milling cutter would be much better.
You may be able to hammer it to fit over the rounded oak but the oak will have to be attached to the counter pretty well. The crimps will form as a series of wide then narrow widths across the open side of the pipe.