1. I have a spare laptop from 2014 (Acer Aspire E14, E5-411 model) but it only has 2GB RAM and 500GB HDD. I do have an external 1TB drive though. Will this setup work?
Even if you can run a node with a laptop with 2GB RAM and 500GB HDD, it will be very slow. And when I try to run a full node, the block size has been about
751gb till today. And my laptop is i5 8th Generation ram 16gb. To run a full node, I upgraded the SSD to 1tb. I am giving a screenshot of the full block download size below. i recommend you to must use
SSD included device which processor is also updated for fast sync .

2. Is there any benefit or difference in running a full node vs a pruned one, and what should I go for?
This is a great learning opportunity for me and I am planning to run it for as long as the laptop can. I would like to hear your thoughts and advice.
Pruned node requires less storage and running a full node requires more storage as I mentioned earlier. And with Pruned node you can give the command how much you want to keep in download according to your storage. And running a full node makes it easier to run lnd and peer connection can be easily done. Apart from that, experts do various other advanced work. Which node you run depends on what you will use it for.
3. I want to replace the OS with Linux but I've never used it before, what distribution is recommended?
This is a great learning opportunity for me and I am planning to run it for as long as the laptop can. I would like to hear your thoughts and advice.
I think you might be thinking of running lnd.
With Ubuntu
Complete GUIDE for Lightning Desktop Nodes tutorial by @Satofan44's. It's really a great job.
since most people are more familiar with Windows, another tutorial LND node on
Windows for Lightning Network - Beginner friendly. 4. Is it necessary to use Tor?
This is a great learning opportunity for me and I am planning to run it for as long as the laptop can. I would like to hear your thoughts and advice.
Tor basically helps in peer connection with privacy . I can't go into details about this but even if you run pruned node you can still connect to peer using Tor. I tried this but failed so I ran a full node.