The first time my husband and I ventured into Morocco was from from the ferry port at Tarifa, Spain We took the 1 hour ferry that goes directly into the port at Tangiers and stayed 2 nights before returning Spain to continue our trip. Some people seem to get turned off by Tangier. Thy was not our case! It was culturally fascinating and it made us want to return and spend more time travelling deeper into the country. Despite having a love/hate relationship with Morocco, we have returned twice (2017 and 2019), with each trip lasting at least 2-3 weeks. We have been to Marrakech, Rabat, Fes, small towns along the coast and small towns inland. All our travels were done independently using trains and buses. On one of the trips, instead of taking a bus from Fes up to Tangier (to cross to Spain), we used a driver recommend by the owner of the riad where we were staying. We found Morocco had a very good rail and bus system. Of course there is a high degree of harassment from touts in Morocco but overall we felt safe wandering the souks and medinas by ourselves in all the places we visited. On a 3 day tour, depending on your mode of transportation you probably could see one place as 2 of those days would be spent travelling ( it sounds like you would be going back and forth from Spain?) If planning an independent trip one website I would recommend is Rome2Rio. Plug in where you want to start and finish and it provides links to travel options and information about distances, schedules and times etc. BTW, we were in our late 50's the last time we were in Morocco and we are healthy and fit.