The following may be of some use to get you started with a server:
You should test everything normal and above and below normal Y Limits.
I loaded the cubic chunks mod into single player and successfully played single player with the following mods:
using MinecraftForge version 220.127.116.1107 for Minecraft 1.12.2
The mods files are on https://minecraft.curseforge.com/mc-mods always click on "view project page" then on the "files" link in the menu for the correct downloads for your versions of minecraft.
The cubic chunks mod does not seem to be found on curseforge.com when I just searched for it! This is a problem. The jar file I have was given to me by someone else and does work. PLEASE would the care takers of this mod please post usable versions on curseforge.com and go ahead and mark them beta versions please!! Their DISCORD seems to have the latest downloads under INFO. see also this link https://jenkins.daporkchop.net/job/CubicChunks/
Minecraft forge is at http://files.minecraftforge.net/
Of-course for the sake of links Minecaft can be found at https://minecraft.net/
When you are logged in to minecraft.net there is a download link.
possibly after logging-in try https://minecraft.net/en-us/download/alternative if you wish.
Perhaps variations of this or even newer versions of this might work.