Cab floor/brace/pillar replacement process

[SixNiner]

Hello to all from a new member! Excited to be starting with my first build project, but was not excited to come across all the rust I have found on my '69 C1500 longbed. Most of the floor has to go, 2 of the 4 outer braces are gone to the point that I couldn't tell what they were, rear cab extensions aren't even there anymore, and the front pillars are shot as well. Outer rockers are junk along with the kick panels and cab corners. AKA YIKES for a new builder!

Unfortunately, I've already taken the passenger door and outer rocker off without bracing first so I need to do that next. But then what? I've been reading a TON and it sounds like a bad idea to cut it all out at once. So do I start at the interior-most part of the floor and work outward? Or just scrap the floor and buy the whole floor with the braces attached from somewhere like LMC truck? If I do that, do I tac weld it in place until I get the pillars/rockers/cab corners mocked up before welding?

Gonna try to start a build thread to keep it all straight but this one may be a bit out of my league. Any info is greatly appreciated and I will certainly KEEP RESEARCHING!