Hey John, welcome to the forum.
Not sure how much you know about the Costa de la Luz, so hope I don't bore you with information.
Here goes, Costa de la Luz is separated into the Huelva Province and the Cadiz Province, Huelva Province goes from Seville to the West as far as the border with Portugal, taking in places such as, Matalacanas, Donana National Park, Islantilla, Isla Christina, Isla Canela (Ayamonte), and many more places in between. The Cadiz Province, runs South of Seville, and along the coast East towards Gibraltar, taking in Arcos, Lebrija, Sanlucar de Barrameda, Cadiz, Medina Sidonia, Jerez, Vejer de la Frontera, Chiclana, Tarifa. Wherever you end up, they are all lovely places, that in my opinion offer the "real" Spain, were doing your utmost to speak the language is the way forward.
All of the above places are coastal, however, places like Lebrija, Vejer de la Frontera, Jerez are all within 15-30 minutes of the coast line. In all of the above places you will find lots of properties to rent if you wish to self cater. Jerez is just a fabulous mini Seville (so I've been told, not having made it to Seville yet) and has a lovely bus tour of the town which is a must to get your bearings, but ensure if you're on the top deck (and you will be), DO NOT sit on the left hand side - if you do, be prepared to duck quickly in order to miss being hit by the palm trees!!
It all really depends on the kind of holiday you're seeking and whether you will have transport or whether you're relying on trains and buses. For instance I know that the train service from Sevilla to the coast is very reliable and stops at Lebrija (very pretty old town) and obviously Cadiz and I believe the system continues along the coast to Tavira (but I stand to be corrected as it's a while since I've been in that area).
Now should you wish to enjoy the Costa de la Luz and take a bit of travel into Portugal, you can do no better than staying in Isla Canela (Ayamonte) or Isla Christina. Ayamonte is the last Spanish town before travelling over the Guadiana into Portugal (via the bridge with a car or the ferry on foot), to Villa Real do San Antonio, trains from Villa Real go direct to Faro, or you can travel by car to Tavira, Monte Gordo (very touristy), Castro Marim (just over the border) has a lovely castle & ruins that are pleasant to visit.
Apologies for rambling, but just thinking off the top of my head, if there's anything else you'd specifically like help or advice with, do post the details and I'm sure we'll all do our best to help.
Regards, Scoya