I'm looking to setup a full node on an old computer.
Specs: 4gb ram / Core 2 Quad / 2.8 GHz
Up to a few years ago, I ran Bitcoin Core on an Atom netbook with HDD and 2 GB RAM as a backup. Syncing took a long time whenever I turned it on, so eventually I gave up on this.
Your setup should be fine, especially if you keep it online all the time. If you're using a HDD, the initial sync might take quite a while (at least days, possibly weeks). Obviously, installing SSD and more RAM would improve this, but if you just want to use what you have, it should work. It will probably help to increase dbcache in Bitcoin Core's settings to as much as your system can spare. Mind the swap file, it will compete with verifying blocks on disk.
From what I've seen (but never tested myself): Linux should sync Bitcoin Core faster than Windows.
It's good enough, just make sure you have lots of free space (at least 400GB)
With 400 GB, you'll last only a few months. A couple hundred GB more will be enough for the coming years.