In order:
1) Yes, you are. Your character will suck to lowest sectors of the abyss.
2) Arcane Archer requires 1st level arcane spells. Think Bard, Sorcerer or Wizard. Sorc or Wiz would be your best bet, as you would technically only need 1 level in either class. The Arcane Archer (AA) class setup in NWN and NWN 2 is screwy, and therefore it is nearly useless to have spells with this class in this game.

If you go cleric, you are being counter productive, although it isn't impossible.
3) Practised spellcaster doesn't work, unless there is some mystery update beyond the 3.84 patch I have I am clueless about. So, regardless, ignore that feat. However, you are completely off in the casting. In order to use the Quicken Spell feat, your spell level in the spell you apply it to increases by 4. As a wizard, this equates to an increase in 8 levels of wizard that you need in order to use this spell on a spell you get. For example. You can cast Magic Missile (MM), a 1st level spell as a 1st level wizard. You gain access to 5th level spells as a 9th level wizard. When you reach 9th level, you can apply Quicken spell to your 1st level MM spell and cast it as a free action, but it will have the same cost as a 5th level spell.
It's a lot to take in, I know. If I lost you, just nod and say "I shall ignore the Extend, Empower, Maximize and Quicken spell feats in the game."
4) What is the benefit in your proposed build? Nothing. Your concept is completely counter productive in every way. The benefits in multiclassing however, are that certain abilities are better than others. So, for instance, it is a bad idea to take odd levels in the Fighter Class, as you get a bonus feat every even level as a fighter. So, you take even levels unless there is some super important reason not to. It takes a while, but once you get familiar with the classes, you'll get the hang of it.
5) Class skills only count as class skills for the level you are taking. Meaning, if you are a cleric at level 5, when selecting skills at level 5, you have the cleric skill set. Purchasing rogue skills at level 5 will cost x2 the standard cost when leveling as a rogue.
6) I am not sure how it works in NWN, as I really don't feel like dealing with creating a character just to see what they did in mutilating a cleric Domain for this game. You are supposed to simply gain Bluff, Disguise and Hide as class skills in DnD. Meaning, they cost the standard cost for skill improvement as a cleric for you now, rather than the x2 cross class cost. Whether the developers changed this in NWN is beyond me. Disguise isn't a skill in NWN, so I am assuming they might have.
I didn't mind reading. As you happened to have taken the time to ask specific questions, it made me want to provide specific answers to said questions. It restored my faith in gamers around the world.

People that think they can ask a rather general and incredibly limited and lazy question seem to believe they will receive miracles in response for some reason.
As for a build, what are you trying to accomplish? From the looks of it, you would be better with an elven Bard/AA. This would give you spells to boost your abilities and healing spells, some rogue skills, and the ability to enter into the AA class. Not to mention, a halfway decent ability to attack and the ability to wear light armor without ruining your chances to cast spells. If you take the Battle Caster feat, you can apply that to Medium armor, if you happen to gain proficiency in medium armor anyhow. A level of Fighter, or 2 levels in Ranger would do wonders for the build in that case.