Would a full blown mage be too difficult to play as in legendary mode starting from level 1???
Also, a side question, does legendary difficulty change what types of items/gold are found, stole,etc?

I personally find Mages to be very boring..

I would not start as a Mage on Legendary. That's just pain and suffering.

And no, difficulty does not affect what loot you get.

You mean, raising the slider to legendary as soon as you configure and name your character, right before going to the chopping block in Helgen? It's possible, although no matter how well you manage your magicka, expect shortages. You can solve things once out of Helgen, by investing on alchemy for magicka and magicka regen potions. If you're going to use destruction, fortify destruction potions will come in extremely handy as well.

Now, whether anything above expert is worth the effort or not... that's for you to decide. The only thing affected by the difficulty slider, is the damage you deal and the damage you take. No changes in loot and gold.

I'm doing it. I'm up to level 31, I think. Like 170 in health, the rest in magicka.

It's rough at times because a lot of things can one shot you even with a flesh spell. I use conjuration a lot to take the heat off me. Illusion sometimes too. On Adept playthroughs I never needed fortify destruction pots or Elsweyr Fondue but I find myself using them during boss fights now. I get a lot of use out of Highborn too.

It's doable though. Using armor instead of Alteration would make it a bit less annoying.

On console they are incredibly boring, but on PC I have grown to love them much more. Too much pausing time to switch spells on console. I just hotkey 8 of my favs now and get going!

But Alteration plus armor is even better. Give you that little extra damage resistance. Plus, alteration has breathe water, paralyze detect life and detect dead, plus telekinisis. Not to mention Transmute Ore.

Alteration plus armor is okay if you're no where near the cap. As you approach the cap, it becomes less useful. +100 AR for fairly high cost isn't great because you have to constantly manage magicka.

Even if you forgo flesh spells, you can still use the other ones.

Anyway OP, running around with 350 AR in robes is hazardous to your health (Dragonhide is too annoying to keep up all the time). Surprise Sabre Cat attack? Become Ethereal and run like hell. Otherwise you're dead. Eventually you may become paranoid like me and use Detect Life all the stinking time. It's a fun and challenging way to play, but I did rage quit last night when an Ice Wraith just TOUCHED me and I died. Those ****ing things...