You're very welcome and thanks for the good wishes.
Yes, that's right, you should be looking at missing no more than 20 questions per section on the practice tests. 300/400, but according to my calculations you can miss 140 qs and still make it, of course there are no scores anymore, so I don't know if that has changed....
I just did one practice test due to time constrains, but it helped me gauge my knowledge.I managed to get a good score and it was very similar to the one I got on that practice test, so you should definitely practice as much as you can.
Good luck with your part 1.