It is a bug that scorpions are so strong.
You need Repair at level 5 to get the most value out of trade equipment (not that it is hard to get gold, eventually), as well as fix 1 durability items.
Summoned rats are a good distraction, since they provoke opponents into attacking them.
Even if the effect/mana is the same at higher levels, the effect per time is better after boosting the skill/spell. For Meteorstrike, though, from your numbers the damage/mana is increasing (4+10 to 5.3+12).
Enemies can wander away if they think you are dead, or turn their attention fully to any summons or resurrected creatures, allied NPCs if there are guards nearby, etc.
Deathly Disks can be very effective, especially used in close quarters. It also does physical damage (like Hell Spikes), so can not be resisted (though the survivor's Curse skill can take care of resistances, one target at a time).
There is an XP bonus when defeating opponents above your character's level, and a decrease if they are below (down to zero about 8 levels below, IIRC).
When skills are maxed, they should remain maxed if there is a level reward from a quest; IIRC there should be an error then trying to use a skillbook.
Restoration potions can be bought or created with Alchemy, and after you get up a few levels give much more of an effect than individual health or mana potions. If you don't mind the time it takes, that is one of the uses of Heaven's Gift (at level 2 or 3, when you start getting regular sized potions, as long as you have a decent mana supply, casting the skill repeatedly should usually give you at least one regular mana potion before you run out, to restore what you used up, and then the rest of the potions, gold and minor loot are profit).
The Spell Shield and Aura of Guarding spells can augment armour. In the elven village in the Dark Forest the bow merchant there sometimes sells mithril armour, which lacks the strength requirements of other breastplates.

Unfortunately, there aren't any mods, other than one for larger fonts.