These posts are not meant for permanent installation. You should use these to raise the problem area in question, then install a permanent support at that elevation, then remove the jack post.
No, you should't use these. You should properly frame support underneath the 8' section. These are not meant to be the primary structural support. This is why their installation instructions say "additional support". The only thing I can say for sure is that these posts would not fly as your primary support for load-bearing wall using the NYS Residential Building Code for what it's worth. Code Section: https://codes.iccsafe.org/content/NYSRC2020P1/chapter-6-wall-construction#NYSRC2020P1_Pt03_Ch06_SecR602
Tempature should have little effect. They are made of steel and will contract or expand with heat or cold but than so does your house. I dont think you will notice 1/32 of an inch.
Hi there, yes these are very strong. A few of them supported part of my house as we were doing some serious structural work below the roof. As everything, it comes down to common sense to have them standing straight and in sufficient number, mindfully placed. No worries, these are professional scaffolding grade.
Not in my closest store
It can be adjusted in place. It's a jackscrew kind of thing.
I recommend replacing them if they have been leaking rusty water for that long. The post structural integrity may be compromised.
No, it doesn’t extend to 10 ft.
yes use flagstone under bottom and 4x4 board on top
NO IDEA. PROBABLY NOT