She’s just a bit dirty but looks like a solid starting point. That rust does not look concerning at all, I’d say surface rust at worst but you’ll know more once you get more familiar with the underbelly.
I’m in the midst of a garage restoration of a 96 K1500 2 door Yukon GT, and this truck spent a total of 12 years in storage on the Oregon coast before I got it. Everything (literally) that was unpainted has scale, pitting and discoloration. I’ve been slowly replacing rusted parts here and there, but fortunately for me it was largely unused while it was stored and is all original (even including the spark plugs!).
I’d pay close attention to the metal brake lines and fuel lines, if it’s been in a moist environment those are some of the first things to rust out. They were untreated and unprotected steel from the factory so if they are compromised, that may be one of the first things you might want to consider replacing. A good stainless kit is not cheap, but these are one of the most important systems in your truck so they deserve attention.
Most of the rest is just going to be manual labor- scrubbing, scraping, brushing and cleaning. Fortunately for you, elbow grease is free!