arrua: Looking at the companion list in gamebanshee, the classic version of BG2 has 4 thiefs out of 16 recruitable companions: Imoen, Yoshimo, Nalia, Jan Jansen.
More than enough.
dtgreene: Baldur's Gate 2 SPOILERS ahead:
Unfortunately, that list is misleading:
* Imoen and Nalia have both dual-classed away from thief to mage. This means they can't level up the thief class, so their thief abilities do not ever improve.
* Jan Jansen is a multi-class thief/illusionist. So, his thief abilities will improve, but not as fast as a single class thief.
* That then leaves Yoshimo, who is a single class thief, albeit with a kit. The problem, however, is that (and why I put a spoiler warning on this post) he betrays you mid-game and then plot dies. If you wait until after that point to recruit him, he will be dead and won't be recruitable there either. Hence, Yoshimo doesn't count because he is not usable for the rest of the game.
As a result, no the game does not provide any good thief options; there's no single-class thief who is usable in the later part of the game.
arrua: The Infinity engine D&D combat system is very good. The combat can be paused at any given time. Making it fluid and fast, while being tactical and fairly complex, without being annoying and stressful. I can´t bear real time strategy combat games. And this comes from someone who doesn´t like the D&D rules much.
dtgreene: The combat pausing destroys any fluidity the combat might have, and it doesn't provide the rhythm that turn-based combat provides.
Also, at low levels combat isn't that fast, as a character can swing for 6 seconds and the game will make only one attack roll for that character. (This is also a case of misleading animations.)
There's other problems with this battle system, but I have to go now.
Imoen and Nalia can detect traps and deactivate them without any problem. Locks too. They don´t need to level up unless you want a thief specialized in stabbing enemies from behind. You were talking about traps, so my point stands.
Same with Jan Jansen. In fact, I feel like the character wastes losts of XP´s in his thief class. Those XP´s would be much more useful spent in his wizard class instead.
Related to SPOILERS
Yoshimo counts because you can keep him for the majority of the main campaign. Then, you rescue Imoen, who is as good as any thief can be, unless, again, you want a thief who can stab enemies.
NO MORE nothing related to SPOILERS
And if you want a character to stab enemies and deal good damage, you can recruit Valygar. Not my thing, by the way.
So, yes. Whatever you might want, you are well covered.
About the combat.
There are lots of combats in the game. If the combat were turn based, the game would be boring and endless. With the pause button, you can make the combat part of the game as fast or thorough as you might need. No need to pause against low difficulty enemies. But you can pause the game as many times as you need to be able to give orders to your characters when fighting against boss enemies or groups of enemies with wizards.
At low levels a simple puny bear is a boss fight. :D Put the bear to sleep and problem solved. XD
In BG2, such a thing doesn´t happen if characters are decently built and equiped.