No. The cost for each reward is all-in; there's no hidden extra for postage. (I may come to regret that, so take advantage while you can.)
No problem. Just pledge a multiple of the reward level. So if you want two signed copies, pledge £100 instead of £50, for example.
Yes. Once the backers have received their colour hardcover copies, a black-&-white paperback edition will go on sale to the public. So expect that towards the end of 2019.
Don't see the answer to your question? Ask the project creator directly.