How big could be an obj file in MB in order to load? is there a limit of memory or meshes? Or it depends on the machine memory? I’ve a core I9 and 16 GB ram
16GB gives you A LOT of room 
The main question will quickly becomes how fast will it load 
Never mind, my mistake. tried to loop render before scene was complete. Sorry.
How could be a mesh with key “up” with the field “_isDirty” marked as true, become a normal mesh after loaded from obj file?
You are going to need to provide more info a repro for instance