Hello everyone!

Roughly how many points in search/open lock/disable device do I need for each area/chapter?

Edit: I didn't catch the typo in the title until I posted this. I'm a little sleepy at the moment. I apologize.

You only really need about half maximum ranks. There are a couple traps that will be a little tough and will require you to retry repeatedly, but everything was at least possible to detect/disarm/unlock with half ranks. As a result, I consider the Rogue completely unnecessary in IWD2 and you can just have anyone with sufficient skill points (like a wizard) pick up these skills cross-class.

Thanks!

Also, it's worth noting that a multi-class character with 1 level in rogue can max out any rogue skill, given enough skill points. It will still take 2 skill points per rank, however. (This is assuming this aspect of the rules is implemented accurately, of course.)

After a few levels, wouldn't the character get an XP penalty? I think the manual said that if there was a difference of four levels.

Not if one of the classes is that character's favored class. (Of note, for humans the highest level class is the favored class, so feel to take one or two levels in as many other classes as you want (subject to the limits imposed by the implementation).)

You can also, of course, get more XP by deliberately keeping characters underleveled, but that can be considered an exploit, especially since the game fails to implement the rule that tends to limit this strategy. (In D&D 3e, you can't have enough XP to level up twice; in IWD2, you can.)