Just secure the ₿ blockchain for starters everything else is step 2

You can run both. Start running it as a bitcoin node. You can choose either core or knots. You can add lightning later if you want. I was lucky and got a used m710 under 50€ but had to flash the bios. I guess a fully operational one would cost you about 100€. I would go at least woth an i5. Ram can be upgraded later. 2TB ssd about 200€ new. So you should be able to build it for about 300€ total. Maybe less if you find another mini pc. HP has also a good series called prodesk or elitedesk

Start9 is free. Thanks @56a6b753…f645b727 legends 🫡

Lenovo m93p is a very cheap alternative. But it runs a little hotter and needs a bit more power. Its very cheap, i started with that, but it’s more fun with a little newer machine in the long run.

i3 around 7th generation should also be fine