Question Advice on making a really large model?

There doesn't seem to be a particular good category for this kind of question on the forums, so "General" it is.

I'm looking for any suggestions or pitfalls to avoid when creating a very large model. By "very large", I'm talking about something that's several thousand units in diameter. For example, modelling a small planet, with hills/mountain/pits. In this case, the object is roughly spherical, but not exactly. So, using a Terrain for this doesn't seem viable.

I'm aware of floating point precision issues, and I'll be keeping things reasonable in that respect. But I've never made a model that's several thousand units across, and I'm curious what kind of issues I'll naively run into.

The naïve approach would be a single giant model with LODs. But than as you got close to it, it would be rendering high-res model for the whole thing, not just the portion you're close to. So perhaps breaking it into regions, with their own LODs, so that only the closest one is actually using LOD0. But I worry this might make really obvious seams along the regions as the LODs swap in/out?

Colliders are also a concern. I'd be concerned about having an enormous collider. But on the other hand, static batching tends to combine things anyway, so maybe it doesn't matter what approach I use for collision?

Anyway, I won't list every concern. I'm wondering if anyone else has modelled a very large object before, and how they approached it. Just searching for this topic doesn't give me any really obvious hits.

 

you can check this guy videos, he knows what he is doing, maybe can give you some indications on how to approach your project