Storage for valuables in Madrid (and general Madrid/Ucles advice)

Hi all,

With Covid-19 and life, I had to postponed a longer walk, but I might be able to fit the 144km of Camino Ucles in my non-camino travel. The recommended 8 days is something I can have at my disposal.
However, since I'm arriving on non-camino travel, I'd have "tons" of valuable equipment that I definatly don't want to carry walking (think of a big bag with 20-25 kg of personal items, such as laptops and computer gear, 2 weeks worth of clothing, a guitar, and so on).

Questions:
- Should I be able to find a very secure and reliable place to store this equipment in Madrid? I want to leave it with zero worrying, knowing that it will stay there for me and for me only. Any recommendation from personal experience would be valuable.
- Will I find "private room" accommodations along Camino Ucles? I my previous pilgrimages, I went mainly to municipal/parish, however with Covid-19 I am not sure how I feel about sharing a room with 12-20 other pilgrims (or more). Should I find accommodations at all? if so, the albergues might be almost-empty anyway (with "private" accommodation as I'd be almost the single pilgrim? ). As a note, I'm tentatively thinking of October 26th (+-3 days) as a starting date.

Note:
I am also open to other suggestions. I'd have about a week available, and I will be arriving to Madrid from Porto (already walked Porto->Santiago, in a week ), but I'm open to other locations as well (my non-camino travel is in Porto)
Ideally I'd like to get a certificate (like the Santiago's "Compostella") of my walk.

Thanks in advance for sharing your knowledge with me