I hope the OP's tips are usefull for some would-be mages. Just be aware, that the OP is wrong on a number of things.
1.There are more spells than just muffle that will level your skill out of combat, detect life for example will level your alteration any time you use it within range of something, even non-agressive NPC's. You can max out (at least) illusion and alteration in a short while without ever leaving town.
2. Rune spells are Destruction not Conjuration
3. Race is a preference not a requirement, you don't need to be a Highelf to own the game as a pure mage on master difficulty. +50 magicka is nice, but really makes little difference past level 20. There are multiple ways to play a mage and most races can be successfully played as a pure mage. My level 45 Breton stomps, with 2 summons and capped 80% magic resistance. I don't need to heal and dragon breath barely tickles. Because I have 25% natural resistance for being breton I only needed 2 item slots to cap my resistance (as an agent of Mara) and was able to use the other enchantemnts to increase base magicka / regen and spell cost reduction. At 530 magicka I rarely run out and regen 18 mana per second in combat. ((530 / 90) * 300%)
4. Alchemy is far more important (reliable and effective) at maintaining mana reserves than using dragon shouts like ethereal form. High level alchemists with +% alchemy enchanted gear can make very strong potions that both recover mana AND increase the regen rate. That said, I often have to sell potions because I end up carrying too many, you really only need them as a crutch in boss fights, most skirmishes you should be able to finish without relying on potions, shouts or 1/day powers.
My favourite potion:
Spoiler
Jazbay Graqes + Red Mountain Flower + Firesalts
5. Robes are NOT a requirement for a pure mage, with and without enchanting you can get light and heavy armor apropriate for a pure mage (-%spell cost / +% mana regen). Shield spells will stack on top of armor, just don't take the 3 perks in alteration for the shield.
6. You can use destruction effectively without ever using the overcharge perk. Stagger is nice but not a requirement for a pure mage when you can use illusion or conjuration spells to disable enemies. shooting lightning from both hands independently is actually more mana effective than using overcharge if you can handle playing without staggers. Overcharge costs 2.25x the mana for 2.15x the damage. From a damage per mana perspective its cheaper not to overcharge, you should only overcharge for slightly stronger alpha strikes that garuntee a kill (where 2x damage won't) , stagger or cool-factor, otherwise your wasting mana.
7. Healing potions are only needed in emergencies, if your using Illusion or Conjuration spells for crowd control (2x Demora lords ftw) you really should not be getting hit, period.
8. Having Conjuration or Illusion higer than your destruction is perfectly viable its all a matter of preference and playstyle.
On a misc. note to other posters and readers;
+Magica regen items DO work in combat, its been proven a number of times. Any one that did 5 minutes of testing would be aware of this.
Please for the love of all that is magical, stop spreading this false-hood.