Official Routes to obtain The Compostela?

None of the routes are really coastal. Some sections of the coastal route in Portugal have a fair amount of water views, and the same is true of a few of the sections on the Camino del Norte. But Santiago is inland, and the final 100 km of all the caminos is without substantial water views. July is busy on the Camino Frances, so expect crowds; however, it is the benchmark camino if you are only going once. Consider it (and prepare mentally for all the other pilgrims).

Hola and welcome.
If you check out an on-line guide such as Gronze it will give you some idea of the routes and how much is near the coast. The Norte is between the mountains and the sea with some options to walk the E9 alternative routes to be nearer the cliff tops. As Falcon says all have inland sections and July is busier. There will be many non-pilgrims also on the coast as it is holiday season. Gronze has sections on each Camino, with outline maps. CSJ have guides (no maps) with clear instructions and also alternatives given, plus suggestions for accommodation as well as the albergues. The Cicerone guide to the Northern Caminos had information, mini maps and some accomodation suggested as well as some photos.
Searching the different sections of the forum will aslo help you to decide which Camino calls loudest to you.
Buen Camino

If you tell us where you are from, we can tell you where to get your Credencial from at home ;-) Then you would have one worry less. Buen Camino! SY