I'm playing on a server with additional difficulty settings, which means you most likely want a bed closeby if any one player gets stuck somewhere at night (we have monsters form into mobs and being attracted to light sources). 1km seemed too distant, and 500m divides evenly. Also, preliminary testing has determined that running 1km on the road will deplete your hunger (I'm planning to put down 70k MFR road blocks, which make you run incredibly fast), and we don't want players accidentally running too far and dying due to starvation. Also, the cost of safehouses is almost negible, 3 beds and an ender chest for food and supplies.
Thats interesting, my first guess was something along the lines of a chunk is 16x16 so your "five hundred" is actually 512 at exactly 32 chunks and you're deploying chunk loaders along the road to keep the road loaded (and maybe also farm fields or trenches full of mobs or pipelines full of liquids or the worlds biggest applied energistics network or ...) Or something like each player can ask for a 128x128 "deed to the land" along the side of the road for megaprojects and there's exactly 4 along each side of every road segment.
Our server isn't quite as dense, and people usually settle several hundred meters apart from each other. We try to keep people settled close enough for interaction but far enough away from each other so that there are no neighbourhood conflicts. Considering we have 15km^2 of worldbordered space for less than 30 people, density isn't yet an issue.
We allready have a functioning nether road system for all 4 cardinal directions, the new road is mostly designed for overworld exploration and finding a place to settle for new players. Also, since we're running ATG with Biomes of Plenty, the landscape is truly stunning in certain areas, with rich sloping mountains and d̶e̶a̶d̶l̶y beautiful valleys. Due to the dangers on the ground at night (full powersuit won't safe you baby), there's rarely much exploration going on in this stunning landscape.
Also I'm absolutely running out of big things to build, having set up a 11x11 chunks base with 60 blocks high obsidian walls, and built the majority of the nether roadways. The project afterwards would most likely be a tokamak reactor or something if i could get the thing working in creative.
