Here's my answers to your questions they be not be 100% correct, but I'll tell what I know.

1) I would say about the comics sell less issues now, and yes variants and gimmick covers did kill sales (along with poor storylines)

2)not sure, it seems like there is more publishers out now.
3) hmmm Marvel seems to be over using a lot of characters these days:
4 DeadPool books, 4 Avengers books, 3 Iron Man books, Captain America has 1 book, but quite a few limited series out, Thor has a few series out too. I would say that Marvel puts out more books now but they overuse a lot of characters. Here's one of the main problems with Marvel when they have a movie about to be released such as: Thor and Captain America next year they start releasing more series so they can try and capture that $$$ from moviegoers. But all they do is oversaturate the market with needless comics. I understand they wanna make some new fans and some $$$ of the movies but do we really need: Iron Man, Iron Man Legacy, Iron Man 2.0, and other assorted series for Iron Man? Same goes with Cap and Thor.

4) I'm not sure about writers making more $$ but wasn't that the reason that Marvel raised their prices?
5) could be but Hawkeye and Mocking Bird failed, not sure how well Black Widow is doing. War Machine tanked as well.

What they need to do is streamline the Marvel comic line and refocus some of the series that are not X-Men or Avegers.