Spoiler
1. Scrolls of light work fine if you stand on the last lighted square beside the dark area and read them. They will light up a fixed radius, part of which will be in the dark area. Or you could read them while holding a torch, which permanently lights the area.

2. No effects.

3. Use enough seeds, depending on your Gardening skill, to get three plants in an L-shape (three sides of an herb square). Pouring holy water on a seed doesn't help, but pouring it on an empty square will grow an herb bush some of the time.

4. The classic suggestion: Carry around a lot of large rations until you're Burdened. Even "strained" works (but beware of the rather significant speed decrease). Though you'll suffer some DEX. loss that way, the strength increase is bigger.

5. Depends on what your stats are. If you're Unicorn and your stats need it, eat Keethrax. Otherwise, a PoCC is very useful. Make sure you carry his corpse to the druid (cooking or food pres., or just a fast trip back) right away.

6. It's worth it if you think you can take an emperor lich (or are able to teleport away from one). Dig up the ones that say "great treasures lie here" or something like that.

7. Gems are very useful for gnomes to sac or anyone else to sell. Crystals of (fire, darkness, knowledge) are also useful. Worthless pieces of glass are just that.

Spoiler
Yes, you can read it on the edge of the darkness to light up some of it or if you have a light source read it inside the darkness. then when your torch runs out or you take off your amulet you can still see in the formerly dark area.

AFAIK no.

As many as it takes. I'm no gardener; i just use what the RNG gives me.

Eat ogre corpses, carry enough to burden you (straining abuses DE), drink potions of strength/gain attribute.

Ask someone else; i never do the druid quest. IMHO it wouldn't be, although at that point in the game you prob have enough time to hunt down some methods of removing corruption.

I've never done it so ask someone else.

Depends on the gem and your race. if you're a gnome, IMHO you should sac it (gnome gods love gems). if its a crystal make use of it (knoledge=bless and use, etc., see the guidebook for more details). all others (esp glass) you might as well sell.

interesting think there at the end...