The 'class' presets in character creation only determine your starting abilities/attributes/talents/skills (all of which can be modified) and initial equipment.
Lockpicks can be crafted (needle+needle, key+soap [though soap is relatively rare] or nine inch nails + hammer [nails are also useful for making footwear slip-proof]); trap disarm kits can not be. Many scrolls can be randomly crafted, or skillbooks created by a specific scroll and blank skillbook (with some exceptions).
Any character can use scrolls, etc, and (with an appropriate level of the respective ability) learn any skill/spell. A warrior with one point put into Geomancer, for example, can learn Midnight Oil (useful to slow opponents, or follow up with fire), Summon Spider and Boulder Bash (ranged attack that doesn't require line of sight); a level of aerotheurge would let them learn Teleportation (useful to damage and move out of or into range, and/or onto/into damaging/etc surfaces/clouds) and Thunder Jump, which is a decent way to get into the thick of combat (without boosting intelligence the stun effect will not be triggered as much on stronger opponents, but for a warrior that is just a bonus, anyway).
If you boost intelligence a bit on your rogue, you can mix in the touch range spells.
Opponents do not respawn.
You can hover over the skills on the hotbar at the bottom of the screen, or open the skill window (hotkey K, or the book icon under each character portrait on the left side of the screen).
For a full list,
see here.
Once you get to the Cyseal marketplace, 2 of the potential companions are nearby, and the other 2 not terribly far away, one of whom you'll come across just following the initial main quest (the other requires a bit more exploring).
