I just did this route in April/May, Malaga to Merida, which took me 21 walking days, with a rest day in Cordoba...so here are my thoughts.
Albergues - you can just show up if it's a municipal albergue - you may have to get the keys from the local police/city hall. I stayed in three municipal albergues, and that is what I had to do - though it seems most towns have a municipal albergue, though I chose to stay elsewhere. Note that depending on the albergue you may need to arrive by a certain time to make it easier to get the keys. It may also be more difficult if you're arriving on a Saturday or Sunday, so be aware of that.
Guides - nothing much that I am aware of. I used Gronze as best I could and also these links to the local Camino Associations -
https://caminomozarabedemalaga.com/ ,
http://badajozjacobea.org/
Other pilgrims - It was super quite for me. I saw a total of 7 other pilgrims over the 21 days. The times I stayed in a municipal albergue I was the only one there. FWIW, the route from Almeria, through Granada, is somewhat busier.
Waymarkers - I thought that it was
extremely well marked. Of the 9 caminos I have walked, this was marked as well, or better, than any of the others. I would recommend you consider using GPS routes on your phone. I used
Wise Pilgrim and Gronze also has routes available.
Other thoughts - If you're concerned about the lack of other pilgrims, or really want to have some social life in the evenings, I would point you toward the Portuguese Coastal (which I have done). One of the 'challenges' of the Mozarabe is that on many of the stages there is not any intermediate services, such as a bar/restaurant to take a rest at. I stayed at the municipal albergues in Almogia, Villanueva de Algaidas and Encinas Reales - these were all good, except that Algaidas did not have hot water.
If there are any other questions that I might be able to help you with, please feel free to contact me, or post a question on this 'blog' and I will try to respond.