As the next thing I zapped through Irenicus' dungeon, and by that reached lvl 9. Then drank a potion of speed and a potion of invulnerability, and managed to kill Mencar Peablecrusher's band in the local inn. As always the hardest part was to kill the thief (likes to backstab, and runs away when seriously wounded), then disposing tha mage/mephit who cast confusion.
For proficiencies: while waiting for gaining back the ranger abilities you'll only be allowed to put 1 proficiency point on your weapons skills, so watch out. But after ranger gets reactivated, 2 points on skills will be avaiable again.
As ranger I rised my two weapon fighting to 3, quaterstaves to 2 (I plan on assembling Staff of Ram out of curiosity, but also the only piercing weapon for cleric is in this weapon class), warhammer and mace. During the early cleric-levels I plan on using flails and slings. As weapons I plan on Crom Faeyr + Flail of Ages, but this can change slightly according what I experience. Not that there'd be too much room for changes on the weapon side...
Now I go back and try to find some exp for my ranger and keep some easy exp for my cleric. Will update later in this post if no comment will come.
EDIT1: I went to the Slums to speak with Gaelen, and almost finished the "Free Hendak" quest. Only not finished to spare some easy exp for me as cleric. Then went for Nalia's quest - there are nice exp there ad the Flail of Ages - not to mention you can spare reporting your success to Nalia for later.
In the De'Arnise keep I used oil of speed against the chief guard and the main troll. I avoided the Umberhulks by brewing the dogstew, and killed the golems with the Flail of Ages and the Staff Spear (found on Xzar).
I finished the quest of "Rescue Montaron", and started the quest for the Shadow Thieves what I delay until I change my class as I don't want to find some scripting bug because of alignment-problem or some such thing.
EDIT2:Finally I've reached Ranger lvl 11, and turned into a Cleric. I'm slowly regain my abilities (currently I'm lvl 8).
I basically did everything what I could without possible interference with the stronghold-related quests. For example I've saved Viconia (then said bye-bye), payed for the Cowled Wizards, solved the Skinner Murder in the Bridge District, killed Valeria's band (had to use a potion of invulnerability + potion of heroism + oil of speed here), killed the guys related to theLimiting Wish adventure (I can't cast that spell, so I started a brawl), and went to Windspear Hills to kill the knights at the arrival + the bandits raiding the landlord's house + kill every single monster in the area. I even had to enter Firkraag's lair to kill the orcs at the enterance (killed a Vampiric Mist too what wandered there for some reason).
Part of this was required because I wanned to step level by level as cleric, and not just gain 40K exps at once and step like 6 one time to avoid any possible loss of abilities. Maybe this was being overcautious, but it was possible to do.
After this I went back the BG, and cleared the Circus Tent. Good amount of exp in separate doses, so it is a fine area.
After that I finally could go around harvesting end-questexp, like saving the dryads from Irenicus' dungeon, freeing Hendak for sure, giving Aegis' body to the Cowled Wizards (Bridge district's murder quest) and other minor things.
Now the plan is to find Lilarchor, and do minor errand-quests until reactivating the ranger-levels, then starting chapter 3 on Bodhi's side.
Oh, and I realised my mistake above, GOOD priests destroy the undead. So I'll be as strong as a fully equipped Vicona, but with better abilities!
Too bad strenght-potions are no loger useable. But there are nifty spells for clerics if you watch without all the carzy super-bonuses of an entire part and their equipment. I still wonder how the heck will I have the required offensive output, but we'll see what can be made up.
EDIT3:
I always forget to add this: back in BG1, on the Werewolf Island the Greater Werevolf was not damageable with Bala's Axe (+3 weaponry). Only +4 weaponry worked.
Back to BG2:
As I much needed exp I went first to Trademeet. There isn't that many exp, but it isn't to bad either, and provides some items as well as good story. As I wanned the Efreeti bottle I did not care for the genie-quest - I killed them by the sword after the Druid Grove quest. But on the way to the Druid Grove I went to the Raksasha/potionseller, bought all coool potions, then buffed myself to kill 'em. As they sell an unidnentified potion what if you try to drink you do a save vs. polymorph I think that's a hint to force-attack 'em without even the genie quest. The buff still lasted for the last druid group.
Against the second druid group here I casted Silence.
I still was only lvl9 priest at the end (I stored the Heroe of Trademeet reward for later. Much later), so with a shrug went to Windspear Hills. The most notable difference here was that at a corridor instead of vampires I met mumies.
I actually killed Firkraag too. I buffed myself there with all things on me after a good sleep (like Potion of power, chant, draw upon holy might, champion's might etc.), and with a couple of tries (less then 10) managed to hit the beast with a Harm (reduces hp to 1). Then it was easy. Oh, and just before Firkraag I reached lvl 12 of cleric, so regained all abilities.
My next move was to enter the Temple District and finish all quest for the shadow thieves, then side Bodhi. and that's where I am now.