Question 1 & 3. Yes. My sister owns a HP and i have owned a Epson. The Epson uses different cartridges for different colors. So even if 1 color goes dry it stops the printer till you refill it. Even if it is yellow and you are printing in all black.
The HP's are a bit different they use only 2 types of cartridges. 1 Black; 1 Multi. So it is rare that you will have the issues like a Epson, but i have seen it stop until it was refilled.
As for a printer that can scan slides and negatives v(Questions 5 & 6), this article
proves to be of some use as to why they are not the best choice. If you are looking to have quality.