First time I played through I maxed alchemy. I didn’t put any points into smithing. Second play through I leaned hard into smithing and partly enchanting, and I felt the payoff was way better.
Simply improving your items makes it worth it. Once you get pretty skilled you’ll make some serious sets too!
Well, if you intend to use the potion glitch, alchemy.
Otherwise, it depends on your build. A mage probably won't grow in heavy armor (smithing). Enchanting is pretty great all around. Also filling your own soul gems ( or completing azuras star black) would be good for your income.
My character is a summoner (no necromancy spells use) and your typical mage damage. If I want to kill enemies without being detected I don't mind using a bow. If I'm forced to close combat I will use a dagger. I don't know if I should invest putting perks in smiting because I'm a summoner mage. Question are all robes in the game have no def?
All robes in skyrim are clothing, which have no defense by definition. Only light and heavy armor can have a defense rating. In your case I wouldn't bother with smithing since it doesn't sound like you're really gonna be wearing armor or even using weapons all that much. I'd probably go with enchanting myself since you can easily buy or find most potions you really need and as a mage having good enchants on your robes makes a huge difference, especially if you're not gonna exploit the alchemy/enchanting loop (which I personally wouldn't suggest doing).
The extreme version of this is called the Alchemy/Enchantment loop where you feed two skill-improving skills into one another. But be aware, this is the kind of thing that can end up taking the fun out of a game for some people.
Also, it's worth being aware that because of the way later Elder Scrolls games scale enemies, any time you're working on a noncombat skill the draugr are training.
I have a question how many percentage do players normally use in their armor enchantment just to be fair to the game. For example I want an armor with less magika use of conjuration spells, is 100% good or above 100%-200% is too op?