I've brought a number of "found" and "neglected" bikes back to life. My general approach to troubleshooting is to start from what works, not what doesn't work. On the first go-around, "works" means it works well enough to move on to the next part, in pursuit of a bike that can be ridden.

Anything that can be gotten to move by dousing it in oil, working it back and forth gently, and waiting, works. The first time you witness this happening, will embolden you to finish the project.

When I was younger, I'd try to liberate rusted chains. It was usually possible, but today I'd save myself the time and simply assume that the bike will receive a new chain.

Once the bike can be ridden, you're in a much better position to assess what "bought" or "found" components are needed to make it pleasurable to ride. Some things like tires might be worth waiting to see where and how the bike gets ridden.

Since your bike is from 2008, you don't need to worry about whether it has aluminum rims, a serviceable bottom bracket, and decent brakes. Were I a betting man, I'd bet on your bike being closer to riding than you think.

If you can find a LBS where they are sympathetic to older, less expensive bikes, it's worth forming a relationship with them, and you can always thank them for their advice by buying your tools and parts there.