Should I book ahead for April, 2017?

I don't believe you'll have a difficult time finding a hotel that time of year. However, if traveling the northern route where many of the towns cater to tourists, some hotels may not have opened yet for the year. You could possibly still run into some wintry weather that time of year. Paradors are government run hotels, many in old monasteries, hospitals, or historic buildings. www.parador.es. The bold faced towns below each have parador's in them.

The second part of your question is dependent on what you enjoy doing.

Since you're arriving early in the morning and it should only be a couple hours drive to Santillana de Mar, if you're up to it, there is the town of Cangas de Onis and Picos de Europa national park with the Santuario de Covadonga. In the town is a medieval bridge and there is a cheese market, but I forget which day it's held. The national park is a few miles further down the road. Near Santillana are the Altamira caves. Believe it's a re-creation of the caves now to protect the actual caves.

If you love coastal scenery and small fishing villages, then the northern route make sense. West of Ribadeo is Praia de Catedrais (Aguas Santas); Cathedral beach. further along the coast is Cabo Ortegal with an impressive view of the bay. About 40 miles from Santiago de Compostela is the town of Muxia with a nice rocky shoreline, lighthouse, and small chapel.

If taking the southern route you can leave Santillana and head east a few miles to pick up the A67 towards Leon and Burgos. At the A231 head west to Leon to start heading in the direction you need to go in. In Leon is the cathedral, historic center, a few plazas, and Basilica de San Isidorio. From Leon head towards Ponferrada. Along the way is the town of Astorga with a nice town hall at the Plaza de España, and a cathedral. Continue west and in Ponferrada is the Castillo de los Templarios (Templars Castle) and a clock tower. Down the road is Villafranca del Bierzo with a castle and convent. West of villafranca is Alto de Cebreiro with a round Celtic hut and the church of Santa Maria. In Vilar de Donas is the church of San Salvador while in Alto de Leboreiro is a very small Romanesque church, Santa Maria de Leboreiro. Continuing towards Santiago you'll pass through Melide. Part way through town is the Cruceiro de Melide (oldest wayside cross in Galicia) next to the chapel of San Roque. Last, and only a few miles outside of Santiago is Monte do Gozo, a monument to those who make the pilgrimage to Santiago (Monumento ao Peregrino) every year.

Although I mentioned a lot of places to see between Leon and Santiago, many shouldn't take very long to see. If taking the southern route consider 2 nights in Leon and 1 night in Villafranca since that should break up the drive into manageable distances.

Once you decide on which route you're going to take, use TripAdvisor, Yelp, etc., to see what there might be to see in the towns you'll be passing through. You can also use Google or Flickr for photos of those places, and use Google maps to do virtual drives through the towns.

I traveled through that area last summer, making hotel reservations 24 to 48 hours in advance. I have no idea whether there's anything about the week after Easter that would make that tactic ill-advised. Personally, I'd risk it if I had a car at my disposal. It would be prudent to do some Googling to be sure you're not going to hit a major festival somewhere, however.

I'm also not sure what sort of weather you will have. That part of Spain tends to be sort of cool/overcast/rainy even in the summer.

If you're flying into Oviedo from the US or Canada, you'll be facing a 2-hour drive to Santillana del Mar when jetlagged and quite likely sleep-deprived. There are some interesting sights in Oviedo, but I think you need to head straight to SdM while you can make the drive safely. The latter is very picturesque but quite small. You will probably be able to walk every street in the town on your arrival day. Since it's Easter Monday, I'm not sure how much will actually be open, but picturesque is picturesque.

The town of Comillas, just west of SdM, has at least two significant modernista buildings, one by Gaudi.

There are also prehistoric caves in the area near SdM, entry to which is limited. If you have an interest in the caves, do some research on obtaining tickets ASAP.

When you get back to Asturias, you have a second chance to see the extremely early churches scattered around and outside the city of Oviedo. The historic district is also worthwhile. There's enough to see in Oviedo that it wouldn't be a bad overnight stop.

On the coast north of Oviedo is the industrial port of Gijon, where I enjoyed spending an afternoon. It, too, has an attractive historic district, but it also has some scattered early-20th-century buildings in the neighboring business district. I imagine you could burn a fair amount of time getting into the historic core of the city, and your time is probably better used elsewhere.

South of Oviedo is the major city of Leon, a major destination for its cathedral, which has amazing stained glass. Leon has a very large and pretty historic district full of lively bars and restaurants. I think this would be a good overnight stop.

Southwest of Leon is the town of Astorga, which has an Episcopal Palace designed by Gaudi.

The #1 stop in Galicia is Santiago de Compostela, which is well-covered in guide books. I imagine it's always rather busy, so I'm glad you have your accommodations pinned down there. The historic area is large, and of course there's the cathedral as well. Expect to do a lot of walking.

North of SdeC is A Coruna, another town with a pretty historic district. The weather is often sunnier there than in SdeC.

South of SdeC, I enjoyed Pontevedra and the small border town of Tui.

I considered Vigo rather dull and recommend that you use your time elsewhere.

Galicia has a lot of picturesque coastal towns, but I don't know how lively they will be in April. I found all of these very attractive in mid-summer: Combarra, Cambados, and Betanzos.

You can go to ViaMichelin to plot your driving route. Take note of the roads marked in green; they run through countryside judged to be especially nice.

Thanks for all of the valuable information. I forgot to mention that we will have spent a week and a half in London and Cornwall before going to Spain so we should be pretty much over the jet lag at that point. After Spain, we are joining the Rick Steve's Portugal tour. Thanks for the advice about the Altamira tickets; I bought them online because that is on my husband's "to do" list. We like to do most anything except lie on the beach (walking along the beach is another matter). We are eclectic travelers and we like visiting small villages and looking at scenery and stopping from time to time to see churches, historic sites and museums. The suggestions you listed will help me a lot. I think I will take acraven's advice and book a day in advance. I also think we will skip Vigo and a few of the other "beachy" resort towns. Thank you again for the advice and suggestions. I was worried that the week after Easter might be a school holiday and families from Spain and other countries might be inundating the area. Don't mind the families at all; just want to have a room to sleep in.