i dont think its that clear cut. If the necro comes in undetected and lands a sleep, it is over for the zerk, if the zerk catches the necro off guard it could be over VERY fast for the necro. If they are both expecting each other, well, id say the necro has a slight edge. Unless it is a low hp race, at rank 30 they wont be able to take much damage at all.
Newb looking for good starter character
To answer the initial question, you can actually learn a LOT as a thief. I have learned a ton playing thieves, you learn where to get supplies, you learn about cool supplies you never heard off from robbing others, you learn to run real well when you get caught, and you learn a lot about timing, strategy, and have a ton of fun in the process.
I'm with you. Everything I know about consumables I learned from playing a thief. I.E., importance of, most of the locations, and how much of a difference they can make. You can learn a ton about strategy, tactics and reflexes as well that way. You gotta go for kills rather than just stealing anything and everything though, otherwise you won't learn quite as much. It gets really fun when your oponent knows how and actually takes steps to prevent being blackjacked. For instance, thief verses smart cleric at thirty is a really fun fight.