[greatdane]

1- Can you sneak around without being attacked in say BlackBurrow everywhere at level 10 if you wanted to?

Yep. Activating sneak and hide at the same time essentially makes you invisible (including to undead) and you won't be detected unless a mob sees invis, or in certain high-level areas where some mob types can detect hidden. I'm pretty sure nothing sees invis in Blackburrow, so you should be completely safe there.

2- After the initial backstab, if you're soloing you can still backstab? Have to somehow get behind the npc cone?

I'm uncertain if this server's mechanics are different, but it shouldn't really be possible. I seem to remember that some rogues were occasionally able to get in a backstab by sort of jumping through the mob and spinning around mid-air, but it wasn't very reliable. If the mob is a caster, you can circle around it and backstab while it's castnig, but you'll never want to solo a caster mob as a rogue. As a general rule, you can't backstab a mob that's hitting you. You'll still get a free single main-hand attack by hitting backstab against a mob that's facing you, so it's worth doing if you can't get to its back.

3- When is Sneak effective? Can a level 20 sneak around in a 40 dungeon?

Your sneak skill's level only determines the chance of succesfully activating sneak, and once it's past 100, it pretty much doesn't fail. A level 5 rogue's succesful sneak is as effective as a level 50's. As soon as you have both sneak and hide, you're able to safely explore any area where the mobs don't see invis or hidden.

4- Is the "fun" of being a rogue to Sneak and Backstab? Surely there's more?

As with classes like cleric and warrior, most of those who enjoy rogue do so because they enjoy the feeling of being the best at something. There is a bit of skill to the class, but it's still a pretty simple one. Some people just like doing really high DPS, fine-tuning and optimizing the damage output of the class that has the highest potential for it, and having the relatively unique ability to stealth properly. If you tend to enjoy classes with lots of options and different strategies, you might be better off with something like a bard, shaman, enchanter or a hybrid. If you want to play a pure melee DPS but think the rogue class is too primitive for you, try monk.