I have galvanized that is 50+ years old and a rusted out water heater. I'm certain I've got rust in the service line to the house. I'm looking at replacing what I have with PEX to eliminate any/all galvanized with rust issues.

My approach:
1) Replace existing galvanized into house.
2) Cap galvanized at what used to be line in.
3) Run PEX to manifold, 'T' to Water Heater closet and Water Heater Cold in and old galvanized Cold in. This would allow me to retain the current galvanized cold lines until after replacing the Water Heater.
4) As weekends permit replace galvanized starting with Hot water heater out to manifold.
5) As weekends permit replace galvanized cold pipes.

Questions:
What options would I have for the service line exposed to sunlight and has a hose bib connected? I'd like to avoid copper, just because I'm nervous about my soldering aptitude.

Will I have to remove drywall to stub out for sink/toilet/shower locations (I'm guessing yes).

Is there a way (guessing no) to replace the galvanized without drywall work.

Am I being overly aggressive in my 'solution'?

We are also considering a tankless water heater so I think PEX would also allow this staged replacement process to work.

I have a crawl space under the house which is where I'm leaning on placing the manifolds.
Good/Bad idea?

Location: Sacramento, CA.