I agree with almost everything you said, and you do have great advice there. I just want to point out a few things:
You can create a literally pure Destruction build, as in do not level up any skill ever, except Destruction. Put all of your level-ups into Magicka, only wear robes, only use Destruction. This will cap you out around level 16 or so depending on which race you start with. It is very easy on master to play this way, because your overall level stays so low and enemies level with you, aside from select things like Dragon Priests which are constantly level 50. The game stays interesting if you don't take Impact, like Skoomatrix said, and because you only have 100 health. It's still overpowered on Master, because the end-game Destruction damage scaling problem never happens.
Illusion can be used throughout the game and easily hit every enemy in the game. Let's take Novice Illusion, Hypnotic Gaze, and Illusion Dual Casting. 3 perks invested. Using the basic Apprentice Calm spell which hits level 9 opponents, plus Hypnotic Gaze adding 8 levels, for level 17 opponents. But wait, when dual cast, the spells power skyrockets to hit opponents up to level 37! For some information, Frost Trolls are level 22, and Bandit Chiefs are level 28. You can have this much Illusion power from character level 4 if you have enough Magicka to cast it.
Your only problem with Illusion is that Master of the Mind is a level 90 perk, so you can't hit Undead until then. If you want to hit the most powerful Draugr, a Death Overlord, it's level 45. That means your basic Calm spell from level 4 won't work. What happens if you use Pacify, the Expert level spell? It starts at 20, Hypnotic Gaze gives it 8 more levels, and dual casting the spell brings you to hit opponents of level 61. Dragon Priests are only level 50.
With only 3 perks invested, you can hit level 61 opponents with Pacify, everything in the game is within that level range. With 3 extra perks (up the center to Master of the Mind), you can hit Undead, Automatons, and Daedra.