Running a Minecraft server for you and your friend sounds like a lot of fun! Allocating 4GB of RAM for just two players might be a bit on the high side, but if you want things to run smoothly, it should be fine.
To make your server run even smoother without any lag, you might want to consider a few things. First, make sure you have a stable internet connection and that your server hardware meets the requirements. You can also optimize your server settings for better performance.
If you're interested in adding some extra excitement to your server without changing the vanilla feel too much, you might like "Raboy's Zombie Apocalypse" datapack from
https://modbay.org/mods/655-raboys-zombie-apocalypse.html/. It adds a zombie survival element to the game, perfect for spicing up your vanilla experience!