I think that the nether could be a slight problem. If we say “no nether” that makes lava harder to find, and it also restricts the amount of space players have, which I think will be enough with the 125×125. Personally, I would stay in the Overworld (or would I) but I think a lot of people would enjoy building in the nether.
Another thing to consider about the nether is how screwed up portals are: if a good chunk of the area goes to the same nether portal…someone will be waiting to back-stab you. So, If portals get fixed and the nether area is restricted, I say, go for it.
Probably most important: Potions require the nether, right? If we don’t do the nether, we could replace lapis with…BLAZE SPAWNERS (Don’t look at me for spawning rules.)
I would like to suggest running the first version w/o the nether, to keep things simple. Maybe with a small, hardcore group, running a smaller space, it could be used.