At what point should you separate an object into multiple objects? I've been trying to create single mesh objects lately but I feel like that may be over-complicating the process.
I am currently building a car for the vehicle challenge. Nothing fancy but as I'm working on the details of the chassis I am wondering if I should be separating the object into its "Car Part" objects. Right now the object is the chassis with indents for the trunk, hood and doors. Should I be separating them out and making them child objects?
there isn't exact rule when you should separate objects or not. generally its what is most convienient for you to model and personal preference.
however, some considerations, if you plan to animate mechanical objects, atleast for me its easier when the parts are separated handle everything. in this case you said trunk, hood and doors. those could be their separate object sure.
you can also think of them how they are in real world. they are separated. :)
There is also the advantage with separate objects that you can name them, so you have a better organization...
In 2.80 you also have multiple object editing, which makes it really easy to, for instance move a door, and still have it 'fit'.
Anyway, it's a personal preference what you do. You can always try it and see if things get easier or not. It is not irreversible. You can always join them again.
Just do it in one part. Try and make your care even sexier than they are in real life. Just a thought but if you want to make it in parts have different ports open for each part so you can work on them simultaneously. Try and understand what a work flow is (I'm still working on that myself).
I am new to Blender but I just finished the Course "Low Poly Rocket" which shows how you can create collections in Blender 2.8 and nicely arrange all objects. Once you have something done you can hide it and Insert it with Shift + A as a complete Collection (Single Object). Maybe you can use this on your project? I find this a very professional workflow.