Also remember that the further away regions are very simplified in their rendering, making it much easier to render them since you have low level of detail.
There wont be any need to render any planetary curvature around the player. The Game will be a Flat World pretending to be a Torus to say it in simple terms.
Coordinates themselves will be “offset from each regions bottom left corner” or so, so negative Coordinates are not going to be a thing (if they are negative, you warp into the next Region, hopefully seemlessly)
Block Positions will likely be 16 bit unsigned integers. and also per Region.
Entity Positions will be some form of floating point most likely. Also offset from the Regions Point of Origin