Fellow RLCraft Enthusiast here!
The issue I've experienced is the following:
After completing pre-generation of the world as recommended in the README TXT file that comes with the server pack with the parameters suggested. I would get periodic lag every minute. To be more specific, 2 seconds, every minute. This was caused by the server saving the world file. It is about 100GB and makes sense that it takes a moment to save.

I am proposing: in the README TXT /save-off is recommended to turn off world saving and using a mod to save the world on a more predicted periotic schedule such at 5 or 10 minutes. Currently it seems like Autosave by SonacToker420 is a good mod option for this.

Alternatively RCON could be used to connect to the server and run the saveall command. I use powershell for this maybe rltweaker could handle this too, unsure.

It's totally possible RLCraft is doing world saving in a different way than I am aware of, but I looked hard and couldn't find anything that was handling autosave. I was under the assumption that world saving happened every 5 minutes and not every minute, but that is simply not the case, at least, in Dregora.

I realize this might be just a normal server administration thing that GOOD server operators should/would know about, but I didn't so hopefully we can save someone the struggle. This does not happen if the world file is small or not-pre-generated and the resources for the server in this situation are probably irrelavant as the server runs on an i9 with plenty of resources for 4 players lol.

If you want to turn off vanilla world saving and handle it yourself you can, however its not recommended.

As for the lag, that is mostly caused by a bug with world saving, which is fixed as of 1.0.4 (Which just released.)