I'll also say the game does get quite difficult. I'm a level 11 Khajiit nightblade now, focusing on dual-wielding and I'm having a tough time with a lot of quests. Mostly I do fine if I go up against solo enemies, but groups of enemies fuck me up good. It might be because I'm struggling to stay on top with my gear. I never seem to be able to afford everything I need and most quests give me either staffs, light armor or heavy armor. I haven't received medium armor or a one handed weapon as a quest reward in quite a while.
So, you are playing excactly the toon I'm building. Some advice from the perspective of 21 Khajiit Nightblade:
- Try to mix armor types - get some heavy and light too to build the skill lines. I plan to wear 5 medium/2 heavy in the end, to get most of the benefits from 5-piece set and get additional protection (heavy in chest/leg slots to maximize protection). I think that wearing 7 medium is not optimal (unless you go all for crit/weapon attacks). And anti-CC skill which is available when you reach 22 in heavy armor looks like a must for PvP. Also, beyond level 20 I discovered that it's no longer possible to just use weapon attacks, in dungeons you must use various class skills to survive, which use magicka (and suddenly using some light armor + passives looks like a viable option).
- Get the Whirlwind (requires 14 in dual wield), it's a must have AoE skill for our build. If you have enough stamina (I suggest using two rings with -stamina cost), go Lotus Fan from stealth -> 3-4x Whirlwind and shit dies as flies. Groups up to 4 are not a problem, unless there are healers. Then go stealth -> veiled strike on healer, finish him with 1-2 light attack -> 3-4x Whirlwind and shit dies as flies. Later on morphed Whirlwind after using Drain Power should be even moar deadly.
- Invest in crafting - clothing for medium armor and Blacksmithing for daggers. Plus buy some vendor enchants for 100-200g, this should allow you to be independent in the gear area, even crafted, enchanted on-level white gear with good traits is a life-saver. And repair your armor, it's a must to keep gear in the good shape. Also, look for the crafting stations in the wilds, you can craft your own gear sets with 3-piece or 5-piece bonuses, some are really useful for Nightblades. For example
* Night Silence: (3 items) While Hidden, increase Health Regeneration by 40%
* Torug's Pact: (3 Items) Adds 100 Armor, (5 Items) Reduce weapon enchantments internal cooldown by 1 second.
* Vampire Kiss: (3 Items) Killing an opponent increases your health regeneration by 50% for 8 seconds
* Hunding's Rage: (3 Items) Adds 11 Stamina Recovery (5 Items) Increase weapon damage by 5% when using weapon abilities.
* (3 Items) Critical attacks also reduce the targets armor by 20% for 5 seconds!!! <- this is awesome for Khajiit crit-build, combined with assassination passive, at least 5 medium armor, +5% crit chance passive for dual wield daggers, and Shadow mundus stone (increased crit damage)
Please have in mind that crafting set requires that you have to know defined amount of traits for each piece, between 2 and 8, so you have to invest some time in trait research.