getting local currency on arrival in Tangiers, Morocco

Beats me, but you can find atm's in town. The taxi will take euro and not screw you, but probably nothing larger than a twenty - - and expect change in dirham.

Don't know about the airport in Tangiers, but ATMs are plentiful at the major tourist cities in Morocco. I would not worry about it (personally, I'd also not bother with Tangiers - if you're flying to Morocco and you have more than the typical day trip - and it sounds like both are true - why not fly to Marrakech? - just my opinion). As Ed suggests, Euros (or even dollars) would be happily accepted by your cab driver. If you prefer dirhams, you could always have your taxi driver stop briefly at an ATM on the way to your hotel just in case you don't find one at the airport. They're easy to find, as in Europe.