Well, in my experience the higher difficulty just requires more skill.
Enchanting is probably a skill worth looking into. Apart from that I think Warriors do alright no matter what difficulty. Wizards can do pretty good, if you want some extra survival probability, you could look into a battle mage. But yeah, it's pretty much the same, maybe some extra focus on crafting could be good though.
Pure stealth characters do awesome against NPCs, but against things like Dragons and other big monsters they die pretty much as soon as they're noticed, unless you run away of course. Maybe I'm just playing it wrong though.
But Warrior is in my expreience the characters that become really strong the fastest. My main approach.
50/50 - health and stamina increase
Main specs:
Block
Heavy Armor
One Handed
Smithing
Get that one dragon priest helmet that gives you extra elemental resistance (works great with the block perk), Use spellbreaker, now when you block, you're pretty much immune to elemental attacks. Use the Lord stone, and I usually play as an orc so you get the Berserker Rage which is really good for taking down big enemies.
Hist skin and war cry are ok too. Actually race doesn't matter that much.
Well, it's mainly up to you and what character you want to try. Last time I played an imperial I used heavy armor and 2h weapons, but that was for RP purposes and I never played him on master.
Looking at his skill bonuses if you want to use them to the fullest, I would say either warrior or maybe battlemage. His racial power isn't bad either and could help you get out of a tight spot. It only calms humanoids though.
Yeah, it can be hard to think of Illusion as an offensive class, but Frenzy is your friend, and tons of fun too when you're either far away or if you combine it with sneak.