Eat and Sleep
We have not been able to locate any hotels in Rosetta; spending the night in Alexandria seems to be the only sensible thing to do.
The food situation is better in Rosetta, although the restaurants do not fit the typical tourist bill. Exploring the Ottoman houses, you are bound to pass some of the fish places. Fresh fish are grilled in the streets, and most places have a place to sit down. This might feel too basic for many, but if the fish smells fresh before preparing, there should be no risk involved.
Lonely Planet warns that Rosetta should be avoided if there has been rain, due to "unsurfaced" streets. This apparently is not all true; the streets are surfaced but covered with mould that starts to float with rain. Just leave your finest trousers back at the hotel, and you will have little problem moving around.
Getting back and forth is very easy for Alexandria, as there are plenty of buses and shared taxis running all day and deep into the night.
Getting from Cairo is just a little bit more problematic. The best is to take the train to Damanhur, and then a taxi or minibus directly to Rosetta.
60 km west: Alexandria
230 km south: Cairo