How many are going? Is your accommodation and meals already paid for?
Do you intend buying anything specific, such as leather goods?
Will you hire a car?
Will you be mainly in a big city? If so, they prefer GBP or the USD.
depends what you need it for - food? Buses? Souvenirs? Hotel? Broadly speaking life should be a little cheaper than Spain, but personally I'd take a bit more than I usually spend at home, just for emergencies, impulse purchases etc.
Sorry to state the obvious, but it kind of depends what you want to buy! Are you camping / staying in an all-inclusive / travelling etc?
The only advice I can give is to wait until you arrive there to buy your currency - the rate is set centrally and banks / hotels / BdeCs all have to adhere to it.
They do, but we were there in April and there is some variation in the rate. If you don't have any dirhams already watch out for higher exchange rates at the Airport. Hotel Ali just off Djemma el Fna was the best we found. The 5 of us (2A 3C) ate in the evening for the equivalent of £30-40 in a variety of restaurants. Elsewhere just haggle on price for everything - whatever it is you won't be expecting to pay European prices.
I'd take about 30 euros each per day, but it'll depend on whether you dine at your 5-star hotel or at a kebab stall, whether you take taxis or buses or walk etc.