You must use bows before you become decent spellcaster. Or go melee but I don't recommend it, it sux and Priest is too fragile.
You can become Disciple (2nd tier) in Melee but Journeyman (3rd tier) in Ranged. Win-win.
Best way is to order your companion to stay in place, lure enemies one by one, shoot them with arrows and when they get closer - let companion do his job and help him.
PS. people recommend to play on Hard for better loot/XP/item stats but it's not worth it. Make combat really bad from decent.
Is it normal for a spell to have a 20% chance of working in the beginning of the game?
yes
Putting skillpoints in school of magic, increasing Wisdom and casting Bless helps.
Is heretical magic a decent magic school?
nah, there are better schools.
How do you deal with ranged attacks in the beginning? Orcs and firebats can kill me in about 5 seconds with ranged attacks (which I can't outrun/dodge), whereas it takes at least 20 seconds for me to kill them
Dodge better (get away further from them) or spam magic seals on them.
It also help to make screen resolution bigger to see ranged enemies. Yes, they are nasty.
You need a lot of potions.
To get them cheaper bring herbalist woman her book from orc shaman in orc camp outside of Iron Mines. Don't rush in, try to lure shaman to you and punish him, don't let him talk to you, shamans spells are DEADLY.
Then you get cheap potions and best place to sell loot.
Later in the game there is Holy Ground spell which work as a Lloyd's Beacon spell from Might&Magic games, cast it outside of herbalist shop and come back with Divine Mercy spell (both are Divine Magic school spells).
Best locations at the start? Cementary (two of them but beware of dungeons, plus - one of them have 3 skeletons on the surface that whack the shit out of you if you're not careful).
In dark dungeons use Light from Inq. School.
Then clean Ashbery and Place of Execution.
Last location should be Dragon Rock and dungeons in other maps (they are p.hard, believe me).
Then you can go with main quest line and clean Iron Mines, lot of loot and potions and money.
Some things in the game are useless
Don't put points in
-Identify (doesn't work and Sixth Sense from Inquisitorial School of magic do this better)
-Perception (Light from Inq. School increase perception)
-Flagelantism (Holy Aura skill is better).
Best school of magic?
Infernal. Can spawn Inferial Hounds on Initiate and Dark Mass on Magister.
Pagan magic is also good, with Rain of Fire, Berserk for companion and Shatter and Regeneration.
Area effect spell are da best, later in the game you will encounter some nasty enemies that you want to remove before they attack. Basically - something to clean the rooms.
-Alchemy (perma potions sounds tempting but you will have enough Devil Roots and cash to make them from herbalist).
-if you ran out of gold go to the tavern and gamble, it helps sometimes