Hi Ish,

You've posted a very broad question… it would help to know if you are travelling alone and where or what sort of place you are staying in...

I have been there a few times for very short breaks only (travelled as a couple) and always wished I had more time to explore both the coast and mountains.

I think you are mistaken about Fes (unless there is another one I'm not aware of)… it would be worth a trip there in my opinion, but it is inland, not near the coast.

Essaouira is the closest coastal town and has always been highly recommended.

Sorry I can't help with first hand experience, but when/if I return to Marrakech I would definitely try to include:
Essaouira
Ouarzazate
Ourika Valley
Fes

Marrrakech is vibrant and welcoming, but you'll spend more than you need to on everything if you are not confident and informed. Try to speak a bit of French even if it's just hello and thank you. We made friends with many in the Medina despite the constant sales call and would generally barter from 1/2 price on up (though others recommend starting even lower I don't feel comfortable doing that). Walk away or say you'll return tomorrow if you think they are charging too much.

Obviously don't miss Jemaa el-Fnaa (the main square), food/fruit is excellent, but be careful taking pictures of any performers and even the stalls sometimes…they will want you to pay. Keep lots of small change on hand to tip if you do want to take lots of photographs.

Don't miss having a hamam, even if you are shy. It's a great experience. Not sure how the public one is for men, I hear it's nice for women, but depending on where you stay they should offer it or be able to recommend.

Get a haircut while you're there… just don't be afraid when the barber stick the scissors up your nose! They are highly skilled and do a great job from what I've witnessed anyway.

Again if I returned I'd do more sightseeing, including Bahia Palace and the Saadian tombs.

Always, always agree your taxi price before you get into the car unless it is a driver recommended by your Riad or hotel.

The same can be said of bus tickets… buy them from a legitimate source.

Have fun!