SAT preparation

Can I use the old SAT materials to practice for the new SAT?

You shouldn’t. There have been huge changes in the SAT. Using old materials would literally be a waste of your time. Given that you can use the Khan Academy new SAT materials for free, I suggest you do just that.
Good luck.

How huge are the changes?

A lot - Changes in: Format. Content. Grading schemes, etc.
You also need new strategies and new focus.
Thus, it’s better to use new materials.

I agree that no one should use Old SAT materials to prep for the new SAT.

What other resources would you recommend besides Khan Academy test? Any online practices tests available outside of Khan?

Really?? Because you can totally use the verbal section. With the Critical Reading, I think you can do away with the sentence completion aside that I think the contemporary passages in the old SAT are really helpful. Aside that the writing also tests some skills in the new SAT.

I believe that there are 7 existing “new” tests released by the CB to use for preparation, but correct me if I’m wrong.

Yes the college board has 8 practice tests (they just released a new one) but if you do those practice tests repeatedly you would surely not be honest to yourself about the progress you have made since you might even remember some answers. So what I advice is that practice for the mean time with the real OLD SAT tests for sometime and about some months to your test date you start using the new ones. Mind you it all depends on the time you have