It’s recommended to have a 4Gio and 2 CPU on the core node. But I think this is mainely for building the node. Once built, what are the minimal requirements for a core node? Is minting blocks CPU or RAM intensive ?
My advice is if you go with 4GB RAM then you should also create a 4GB swap file for extra virtual memory. Having said that, the core node is not overly CPU or RAM intensive. I would invest in more CPU and higher RAM on your relay nodes. You can see your relays taking a huge pounding during the epoch transitions. Having enough RAM on the relays usually saves them from crashing.