I think you would get the best results if you go into your current service providers store and ask them to swap your current SIM to an eSIM, as others have suggested.
In almost all cases everything will continue working when you put in the second SIM. You should also get your second SIM locally in Spain or whichever European country you arrive in first. This way they can help you set it up.
Ask them to set your local SIM as the default for data. You can only have one active data SIM at any moment.
Both SIMs can, however be used for phone calls and SMS TXTs. With incoming calls and TXTs you probably won't even notice which SIM they come in on but with outgoing calls and TXTs you will need to choose which SIM to use.
According to recent tests Vodafone has the best phone coverage by a small margin over Movistar but Movistar has better data coverage in Spain (you didn't say where you were doing your Camino). See the report here
https://www.google.com/url?sa=t&sou...0QFnoECEUQAQ&usg=AOvVaw19A7fELmnX1MCPYKM6U1o4
Short answer, no. Unless you plan on taking a laptop or something similar and even then you can create a mobile hotspot using your phone.
Buen Camino