Skyrim – walkthrough and progression.

Interesting topic.

Battle with Atronachs

You'll get tired of it; they don't give much experience. It's easier to find stronger mobs and visit them more often, as they are updated from time to time.

Genocide of the guards

This is immoral; who will protect the city? :) Unless it's in Markarth, where after completing a certain quest, they attack on their own, as certain individuals framed the main character.

Illusion -
Alteration -

I know how to level up Restoration and (apparently) Alteration well. Alteration has the "Equilibrium" spell, which transfers health to magicka, and Restoration has "Healing." In theory, you can level up both skills quite well with these transfers.

Enchanting - enchanting daggers and bracers obtained by developing smithing. It will require more money, but they say that you can even make a profit from selling them.

To reduce costs, it is useful to complete the quest for Azura's Star, but do not bring Azura's Star; instead, go to the tavern in Winterhold and find a mage there. Completing this mage's quest will give you a black version of the star in your inventory, which is essentially an indestructible black soul gem.

And also: is it worth posting the location of all the Barenziah Stones, Daedra, and Dragon Priest Masks in this topic?

This is not pointless. Especially interesting are those Daedric Princes, with whose servants you can fight.

Another question: is the maximum level in Skyrim really 70? According to my calculations, if you develop all skills to 100, you can reach a much higher level.

You are probably right, but if the level scale relative to skills is not linear (although I haven't noticed any non-linearities), then this may not be the case.

If I'm not mistaken, in the upper guide, I described easy development of all skills except Alchemy. I read that you need to buy and collect all the ingredients you find, use the services of teachers, but as a result - a small effect for a lot of money. For example, by studying with Arcadia (Whiterun) and Babette (Dark Brotherhood sanctuary), you can reach level 90, but how do you get the remaining 10? They will be the most difficult to get...

There are so many ingredients lying around in Skyrim that Alchemy=100 is probably not that difficult. But I personally am already tired of potion-making.