Well, the game doesn't -force- you to join the fighters guild. That entire questline is kinda optional... but... it makes sense to join them, for some neat (mostly daedra-killing) abilities and extra XP from the quests...

The classes in ESO are more a matter of what personal magic a character uses - weapons and armor being free to choose as you like. So it depends...
...do you want to cast golden holy magic with fiery smithing and tons of heals? Be a Templar.
...want purple daedric summoning magic, curses and blue lightning? Become Sorceror.
...desire reddish lifesteal, daggerstrikes, shadow summoning fear and invisibility? Go Nightblade.
...are you a pryomaniac dragonlover or do you like stone spells? Dragonknight.

Witcheresque characters, as stamina in medium armor and two-handed sword, heavy on fighers guild skills are easy enough to do for every class.

Hellblazerish characters... well, I would go with a magica-heavy balanced build, light armor (necromancer set looks trenchcoat-ish!) and perhaps dual wielding daggers. Using the dagger attacks as secondary attack while enjoying the spellpower boost from dual wield, and going heavy on mage guild and class skills instead. Maybe a destro or resto staff as secondary weapon. (though that concept would cry for optionsl destruction/restoration weapons... just sayin...) Won't be as optimal as pure characters, but... ought to be doable, and if you enjoy the character, that's the main point, not being super-effective!

In the covenant, bretons are the best for casters, redguards for stamina DPS and orcs for tanks. But that's only if you really are into min/maxing, otherwise play as you want, the racial passives are not -that- big a deal.

I have had lots of fun playing as dunmer nightblade, argonian dragonknight, nord sorceror... you might not get "optimal" with such, but you'll get "close enough" once you learn how to play your build right - the trick is more in selecting the right skills for the occasion then having one FotM build. And between class skills, weapon skills, sould magic, fighters and mages guild... you'll have enough to find your own effective way.

In any case, for your notions... I'd say, breton would make a decent hellblazer basis. Witcher... could be anything, if you like to keep it in the covenant, breton would serve, if you want to spread to have one in each faction, I'd suggest going nord perhaps... and then think of something elfy or cattish for AD...