If you want to browse the forum peacefully, an old Linux PC is ideal.
Maybe, but we are talking about attack on privacy in this topic, and I don't think old Linux PC in enough for that.
And the way we are going in the world I suspect it is going to get much worse in future, before it gets better.
open hardware is also a good solution
There is a website tracking all open hardware, and some hardware wallets released everything in public, so you can create your own DIY version if you want.
It always depends on what you want to do, if you have to look at the forum an old PC with a chip before 2007 and Linux do their job perfectly, then on the internet side you just use TOR -> VPN and you're fine
If you have to hack the NSA, I don't know what the best setup is.
I hope you understand what I mean, there are various levels of security depending on what you need to do