Beastmaster{5} - (2nd and final update)
A lack of concentration gave Mulahey the chance to summon his supporters in the Nashkel Mine,
but a potion of speed ensured I could get out of the cave before he could cast a spell - stealth attacks then finished things off without further trouble.
There were no more hiccups on the way to the Bandit Camp. In the Cloakwood I made the effort to invade Centeol's lair and killed all his defenders, before realising that I couldn't use Spiders' Bane anyway

.
However, the fights there did suffice to get me to level 7.
Arriving at the Cloakwood Mine Drasus was pulled away to die in a running fight. After a long period resting to regain full health Genthore and the mages were scared and shot down. Inside the mine I stealthed down to the bottom level, where the inability to pause properly meant the battle horrors again posed a problem - the second one had to be finished off with a potion fireball after my HPs fell dangerously low.
After resting up again I tackled Davaeorn - this time using stealth shots to get rid of his spells before finishing him off.
After resting to get a second horror ability I flooded the mine and left. Next I went to do the reputation quests ignored earlier. An unintended detour meant Samuel expired before being taken to safety and Melicamp also died, but there was still plenty of gains to be had to maximise reputation.
In the City the tomes were grabbed - the intelligence increase giving the ability to use scrolls - along with the Eagle Bow and Helm & Cloak of Balduran (just sneaking past Degrodel's guards as I had already got my final BG1 level). Most of the damage at the Iron Throne was done with Arrows of Detonation, with a few stealth attacks finishing off the survivors.
At Candlekeep a potion of storm giant strength allowed the tomes to be obtained, but stealth was used to leave all the occupants of the catacombs untouched. A side trip to Ulgoths Beard then picked up the Greenstone Amulet for the sole purpose of getting the final tome from Durlag's Tower.
Back in Baldur's Gate Slythe's chances in a fight were effectively eliminated after a stealth shot with a dispelling arrow. The palace was potentially more of a problem and I considered bringing out the familiar to give the dopplegangers something else to chase. However, with the difficulty of pausing I thought that might actually make controlling the fight even more difficult. Hence I just potioned up (adding in a defensive harmony scroll for good measure) before attacking. The first horror sent 2 dopplegangers running, which was a good result and Belt wasn't too badly injured when the last of the active attackers was bludgeoned to death.
After sneaking through the maze I went straight to the temple and used a potion of magic shielding to protect against traps. Sarevok was hit by a stealth shot with a dispelling arrow, prompting Semaj to teleport out and he was shot down with more dispelling arrows.
Sarevok was then run round a bit before I closed for a melee finish (difficulty in pausing meant I failed to catch the death scene and had to settle for posing with the body using the Final Save).
Beastmaster L8, 100 HPs (incl. 6 from familiar), 300 kills