1) SMC is fine until char lvl 6. Preferably don't get to level 6 there and just find the staircase. Tension rooms in SMC quickly raise your level.
2) Cavernous levels are dangerous in general due to much higher monster generation rate. Try to get to the down staircase asap and return later if you have ~12-15 PV.
3) Easier way is to throw stuff at them until they calm down, iron stuff is common. Using offensive wands works too, rust monsters have no resistances. They are also fairly slow so you can outrun them.
4) It's a good habit to clear the level around arena to only leave the non-hostile ratlings. Monsters in arena are pretty high leveled so it's best to complete arena quest later, when Thrundarr asks you to do so.
5, 6, 7) Avoid bug temple entirely. Don't even go there at level 20 unless you REALLY know what you are doing. Bugs are deadly, super fast, ignore PV and land multiple attacks. To get the rewards from bug temple, you'd be forced to kill MANY bugs, sometimes while being surrounded by them. This is tough and dangerous stuff and it's definitely out of your league, or for that matter - out of any early-mid game character's league. Wizards with 32+ willpower and high DV can hope to clear it with some care but otherwise you need powerful melee attack and very good chance to hit - something you only get later in the game. Also you need lots of speed and it's best to have seven league boots too.
8) That's a wand of magic missiles and it's the common cause of many deaths. The bolt bounces if cast against the wall and will usually hit your char. If it hits once, consider yourself lucky since it's possible to survive, though not with low hp. The deadly part is when you cast it between two walls with you in the middle - you will get hit many times and inevitably die.
9) Forget kranach. This quest is more dangerous than it's worth it. I never do it, though occaionally the reward might allow you to buy something in the black market. It's still not worth it in my opinion and the quest doesn't have any other consequences if you skip it.
10) Poison can be deadly in the early game. Try to get a corpse of poisoning monster and eat it. Typically a spider corpse works. Eating it has a high chance of granting poison resistance. When you face a monster with poison attack, switch to coward mode and try to shoot it or cast a spell. With coward's DV bonus they should miss virtually all of their hits. Potions of cure poison are fairly common as well - keep them around. Keep your eyes open for herbs - alraunia antidote cures poisoning when eaten.
11) There's really nothing I could say about preventing starvation. The general rule is that you should always have something to eat with you. If you don't then drop whatever you're doing and go to Terrinyo and buy some more. Try to predict how long you will last on a given amount of food before you descend deep into a dungeon. Also, consider buying cooked lizards from ratling merchants around arena. Cooked lizards have satiation value roughly equal to large ration, they are cheap and weigh a fraction of a large ration. You can usually buy between 40-100 cooked lizards, 5 gold a piece. They should keep you well fed for a long time.
12) HMV has a high chance of generating stone giants and stone giant lords. They have a big view radius and will often throw rocks at the PC from outside of your line of sight. When first arriving in HMV, set your tactics to coward and if you have shields, wield them in both hands. Once you find out if there are giants/giant lords in HMV, you can try to dispatch them with wands, spells or giant slaying missiles if you happened to find those. You can also try to maneuver around the shop keeper. If done right, a stone giant standing in the shop entrance will be attacked by the shopkeeper if you pick up an item in the shop - but only if you didn't attack the giant yet in any way. Sometimes giants can be tricked into throwing rocks at you and hitting Hawkslayer instead. He will usually proceed to mutilate said giant and will in the process clear your path.
"Hell is empty and all the devils are here."