I keep a spreadsheet of: date taken, PT#, time, score, and comments. I've done over 200 game sections during my practice. I score -0 to -1 consistently and finish most game sections in 30 min or less.
You're in great shape to improve, just keep plugging away on the PTs, do excellent clean test BRs, and use your analytics to point you in the right direction.
I would leave it blank. Guessing an answer right means nothing and will mislead the analytics. Personally I just add .2 points to my total score for each unanswered question when computing my score. It takes out the random element.
I always put it in so I get an accurate score of what I would've gotten on the test. You'll see it on BR regardless so to me it really doesn't matter if it shows up in the analytics since you're spending time with it anyways.
First thing you need to do is to start taking PT on a regular basis! Then, once you have a solid base of scores and analytics, you'll be able to make a good call on which test date is best for you.