I hadn't thought of trying to extend the loan period, doh. I saw the field showing cost of the loan explode when I tried that for things like an engine factory before, so I kind of forgot to try it on the starting car since I usually do the shortest loan period as it's default and I became accustomed to keeping it there. I'll give it a try next time I do some Automation.
I agree about tiny car factories, they really are not ideal. Unless I'm so strapped for cash that I can't afford the upgrade from Tiny plot to Small, I always take at least a small plot so I can upgrade the factory size later. The other reason I start with a Tiny factory is because it's only about $3mil if I remember correctly, and the market is Archea is pretty small so it's easy to over produce at the start. Archea mostly buys budget cars that can't be made for enough profit with contractor engine costs, it's hard to design one without an engine factory that will make much money.
There is one use for tiny factories though: they make a good starting factory for concept or prototypes of models that you tanked the sliders on to engineer faster. Facelifts seem to go much faster and cheaper than the initial engineering on a new model.
I usually scrape up enough cash for an engine factory by around 1950. Going from contractors to a small engine factory is a big savings on production costs though so once it's affordable the sooner the better.
For advertising, I do that eventually once there is some cash for it. You can also get a lot of free advertising that isn't useful for a while if you advertise for markets that don't exist yet; for example Pony. There are a few Other type advertisings in the dropdown menu that apply only to markets that don't exist yet in the nation selected, and if you put advertising into them they are completely free. The % increases on the nonexistant markets increase over time so I think it works. I don't know if when the market opens if it reverts to the set value; I don't recall noticing if it did. It seems like it's probably a bug but I guess it could be that the company you are playing as contributed to the development to the market culture that later emerges, enough to be a favored brand by the customers of that market.