Hi! First off, welcome to the forums! Feel free to ask me or any other forum goer if you have any more questions regarding the forum, or Infinite Flight in general. Or you could simply search your question with basic keywords in the top right search bar, and something will most likely come up. :)
Regarding your questions, pretty much all the planes operate in a similar way, but some respond and correct to movements faster, while others just feel “heavier.” It is probably not that noticeable at first, but after you play around for a bit you will definitely notice it. The 787 is more responsive, and feels lighter. Also, it is perfectly fine to be straight forward, I’d rather someone get to the point than drag on for a long time.
Most variants are labeled relative to size. So the B787-8 is shorter than the B787-9, and the same goes for the -10. This is true with most other planes, Boeing and Airbus alike. For another example, take the A320 series. The A318 is the shortest, and the A321 is the longest. For this type of thing you can also easily search up the plane type (Ex: 787, A320, etc) and go to Wikipedia, then scroll down to variants. That section will almost always explain the differences between them.
I personally prefer the B787-9 simply because it is generally the most popular among real world Airlines, due to its good mix of range to passenger count. It also is the most proportional of the 3 variants in terms of wing and tail size relative to the rest of the body, at least on my opinion.