First of all, you are worrying too much.
You can walk as fast or as slow as you want. You are off the really peak season, so you should have no problems finding room at the albergues. Albergue showers are in single stalls for the most part, but if you are that shy and want privacy and be alone, do not stay in an albergue. Get a room, as they say.
I do not know what you mean by "what's the food like".
As far as the weather goes, you will not see snow. Maybe some frost in the morning. Maybe. Chilly evenings and morning, but not cold per se. You will not need what would be considered cold weather gear. Check out one of the many web weather sites for real research.
I do not know where your home is, so unknown if you mail stuff there from Spain. My best advice is do not bring too much stuff that you nave to mail some home.
If your pack seems heavy, take less stuff. If it weighs over 8 kilos or so, you have too much stuff in it. If you cannot carry it on an airline flight as a cabin carry on, you probably have too much stuff in it.
My best advice is to research Spain and the Camino via articles, youtube videos etc.