I have a doubt sometimes after I build omnios (omni bi), when trying to create a onu ( omni onu -d) it starts downloading packages (around 1.46 GB), is that possible to avoid?

Are those coming from the omnios extra repository? If so, you could offline that publisher before doing the onu.

one of those is ooce/developer/rust

gcc13, etc. If I cancel the onu and offline the repo, it won't cause an issue?