Marrakech is lovely and VERY touristy, so you will be fine. There are two parts of the city - the older, walled "medina" (Old City) and the newer, more cosmopolitan area outside of the walls (New City). I much prefer to spend time in the Old City, but the OC in Marrakech is annoying because they allow motorized vehicles (unlike other Moroccan cities), so you have a lot of gas fumes and need to be vigilant about not getting run over. That said, you will have a wonderful time exploring and just walking around. There is a cool garden (paid entry) in the NC and many excellent sweet shops (Marrakech is know for its cookies). At night, spend some time in the main square of the OC - it will give you the (wonderfully) stereotypical Moroccan experience with fire-eaters, snake charmers, etc. and many, many excellent food stalls.
Restaurants are wonderful and plentiful - just pick one. Buy bottled water, but food is safe (and very, VERY good). Of all the places I have traveled, Morocco is my favorite place to eat.
ATMs are easy to find. Bring a waist-style money belt and just keep a small amount of cash in a snapped/zipped shirt pocket or front pants pocket. Crime is not too bad, but pick pocketing is rampant, especially in the narrow and crowded OC.
Morocco is a primarily Muslim country, so you need to dress very conservatively (long sleeves and long skirts/pants). Do not take James Bond movies as your style guide.

You will see young female tourists dressed in skirts and short sleeves, but you will also see that they get a lot of unwanted attention.
Because it will be so hot, I recommend very breezy, lightweight linen pants and button-down shirts. I actually find that dressing like this keeps me much cooler than having skin exposed and often dress like this in DC as well. Bring a wide-brimmed hat as the sun is intense. You may find that you divide your day for sightseeing and spend a long lunch hour inside in the shade eating and napping or relaxing to miss the worst heat.
You should also bring a lightweight scarf or shawl that you can use as a wrap if it gets cool at night (or in restaurants) or as a head scarf if you go into any mosques, etc.
I am sure you know this, but alcohol is pretty nonexistent except in high-end western hotels. Most Moroccans drink a lot of sparkling water and sweetened green mint tea. Cafe culture (like in France) is huge.