Your sentences are grammatically perfect. The second sentence sounds strange though, but for logical rather than grammatical reasons. It seems odd to speak of "10 cars and more cars" because when you say that, the number 10 serves no purpose. To express the same idea, it would make more sense to say "more than 10 cars" or "at least 10 cars". "Around ten cars" sounds good. It means approximately ten cars. You can say I had "some ten cars". "Some" acts as an adverb modifying "ten". However, you cannot say I had "ten some cars" because "ten" is not an adverb and cannot modify "some".

It should be "I had some ten cars" meaning I had approximately ten cars. That's an odd thing to say though because who doesn't know how many cars they have exactly? 🙂

Then sentence is incorrect. It should be: I had ten cars. OR I had some cars. It is possible to say: I had some ten cars. It's an odd usage - basically SOME in this case means ABOUT.

You have to put ‘some’ before, not after, the number. It’s a rare usage that does not mean exactly the same thing as ‘around’. It conveys more uncertainty. I must have gone to some 1000 movies in my life, but this was by far the worst. (I’m not really calculating the exact number and rounding it off to 1000. It’s just a big enough number to make my point that it was a terrible movie and lets the listener know that the exact number isn’t important and that I didn’t spend any effort in figuring out the number.