Sounds good. If you got stuff you don't need you can always leave it at an albergue. If you need something, you can always buy it somewhere on the Camino. That's something that's not mentioned much on here. You could actually arrive in Pamplona with no Camino gear at all, and step in a sport's shop and come out an hour later ready to go.
I've done the CF twice between July-August. Zero rain for the entire time (SJPdP-SDC). Zero. So maybe ditch the umbrella, unless it's for the sun.
I never brought laundry detergent. I always just used whatever was available. It's only for a few weeks, and your stuff, unless washed in a machine, never truly gets clean anyway.
The meseta portion is nice, but not a desert or something like that as it's often described. It's just a flatter stretch of the CF between Burgos and Leon, and it has a lot of agriculture fields. It also has just as many towns on it as the rest of the CF. So if you gotta skip something, may as well skip that. Same with the first day over the Pyrenees. Yeah, it's cool and all, but if ya gotta skip it, ya gotta skip it. No worries, it's all good. No bad way to walk the Camino.
ultreia