Hi,
Here are the answer to your questions.
a) You need to answer each and every question on the GMAT. Since it is an adaptive exam whose difficulty gets recalibrated based on your answering pattern, you cannot skip a question and come back to it later. The best strategy when stuck is to take a calculated bet, and move on. Don't spend precious time when answers seem dicey.
Our experience is that when you are unsure, you keep spending precious time and are more probable to mark the wrong answer.
You may just be lucky and be stuck on a dummy question, and hence not lose any points.
b) Run a search for 'GMAT score charts' and you will come across tables that depict how scores are calculated.
Magoosh is one source that publishes such charts.
c) Make sure you don't forget to choose the schools where you want to send your GMAT scores to. You can select upto 5 schools before the exam formally begins.
Else, just be relaxed and do your best.
d) There are no clear numbers available on the section wise distribution. For quant, since there are 2 sections, you can assume an almost equal split. For verbal, typically you would get 3 RCs with around 3-4 questions each. The rest can be assumed to have a fairly equal split between CR and SC.
To reiterate, these are all guesstimates.
Good luck.
Best,
Romit
(On behalf of TopTier)