|1) Some types of stars can't support life-bearing worlds, either being too weak, giving off too much radiation, or simply not having any planets in the habitable zone. If a planet is pretty far from it's parent star, it will probably be rather dark, and will not receive enough light to support life. Of course, even closer to the star, the night side of planets will be dark, so you might want to move the targeted location on the landing screen to a brighter area on the day side. I believe type S00 yellow stars and S04 orange stars are your best bet for locating a world with life.|
2) If you're referring to the fuel orb that appears as a glowing ball of lights in the center of the ship, that's only available in Noctis IV CE (NICE), a modded version of the game that changes a number of things. To activate it there, you would access the ship's main menu and go to EXTENDED > MORE OPTIONS > OMEGA DRIVE. It provides infinite fuel though, so it might be considered something of a cheat. : P
3) I honestly don't know all the hotkeys off the top of my head. For standard Noctis IV, they should be found in the manual. The modded versions of Noctis, NICE and Noctis IV+, add a bunch more hotkeys for things, some of which are debug options that probably shouldn't be activate-able by a single-key press, but are. >_> In NICE, you can press F1 for a list of controls, which changes whether you are in space or on the surface. I believe it also comes with an updated manual with more details. For Noctis IV+, I don't believe there's an easy list of keys available anywhere, although they're probably mostly similar to the Noctis IV and NICE keys.