1. Limpets are general purpose devices, they do whatever the controller tells them to do, collection, prospecting, fuel transfer or hatch breaking. You assign the
controller to the fire group and when you fire it the limpet which is released will perform that one function. A prospector is one-shot, fired on line-of-sight. When it hits a rock select it as a target and the bottom left panel of your HUD shows the composition and as you mine it the total percentage will drop until the asteroid is depleted. If you have, for example, a two drone controller you can fire a second prospector at another rock. When you fire a third one of the first two will expire so only two are out there at any time. The prospector will also expire if you fly beyond its range. Using a prospector roughly triples the amount you can mine from a rock, so they are worthwhile if you have space for the extra controller. Collectors will pick up any fragment within their range for as long as they last as long as you
don't actually select the fragment. If you do, the collector will expire immediately after returning it. Sometimes collectors expire early, which is annoying, or hit other asteroids, their collision detection is not very good!
2. There is a default key for "Next fire group". I can't remember which one it is as I have reassigned mine to a button on my HOTAS. Changing fire-groups quickly can be essential in combat. To find it go to Options on the
main menu (not the menu in the HUD) and select Controls and scroll down to find it.
3. The refinery has two areas, the hopper, at the top, which has 2 sections, and the bins at the bottom. 2 bins isn't really enough for serious mining, but it's enough to give you a try-out. I can't remember the maximum you can get in an Adder. Most fragments have two different materials in them which come in to the hopper, are refined, and then transferred to the bins. When a bin reaches 100% it creates 1 ton of the material and puts it in your cargo hold. If there isn't a spare bin the material stays in the hopper, which jams and you get a Resources Unallocated message. You must then manually either vent the stuff from the hopper if you don't want it or vent a bin to make space for it. With only two bins you'll be doing that a lot! (I just checked the Adder: a 3A refinery gives you 8 bins, a 2A gives you 6). Since the 1.4 update the transfer is supposed to be automatic if there are empty bins, but it seems to be liable to stick some of the time.
Looking at the Adder you can get everything in like this:
http://coriolis.io/outfit/adder/03E3E3E1E2E3E3C-1717--02441lC5P4.Iw1+kA==.Aw1+kA==, but there's only 8t of space, no discovery scanner and only one of each type of limpet at a time. The limpets take up cargo space as well so overall you are going to be pretty pushed for space unless you fly without a shield (not recommended in an asteroid field!)
There is a Youtube tutorial here:
https://www.youtube.com/watch?v=EkU-1SJ_7a4 which may be useful.
Ninja'd: but between the two of us and the tutorial you should get the idea!